Python四行代码，利用datetime库。

import datetime
while True:
    try:
        month = ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October',
                 'November', 'December']
        week = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"]
        d, m, y = input().split()
        print(week[int(datetime.datetime(int(y), month.index(m) + 1, int(d)).strftime("%w"))])
    except:
        break

看了下面的答案后，发现还可以更简单，"A"直接输出的是Tuesday这种格式，太方便了。于是代码可以缩成三行：

import datetime
while True:
    try:
        month = ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October','November', 'December']
        d, m, y = input().split()
        print((datetime.datetime(int(y), month.index(m) + 1, int(d)).strftime("%A")))
    except:
        break

人生苦短，我爱python。

import datetime
print datetime.datetime.strptime(raw_input(), "%d %B %Y").strftime("%A")

Python其实只要两行233

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <iostream>
#include <vector>
#include <map>
#include <cmath>
#include <set>
#include <queue>
 
using namespace std;
map<string, int> mp;
map<int,string> _mp;
string months[] = {"","January","February","March","April","May","June","July","August","September","October","November","December"};
string weekdays[] = {"","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday","Sunday"};
void init()
{
    for(int i = 1;i<=12;i++)
    {
        mp[months[i]] = i;
    }
    for(int i = 1 ;i<=7;i++)
    _mp[i] = weekdays[i]; 
}
int main()
{
    int d,y;
    string m;
    init();
    while(cin >> d >> m >> y)
    {
        int mm = mp[m];
        if(mm == 1 || mm == 2)
        {
            mm += 12;
            y--;
        }
        int ans = (d+2*mm+3*(mm+1)/5+y+y/4-y/100+y/400)%7 + 1;
        cout << _mp[ans] << endl;
    }
}

基姆拉尔森计算公式

//隐藏条件就是1年1月1日是星期一，把这个时间点设为锚点
//计算输入的日期与锚点之间隔了多少天
//天数对7取余，所得结果就是星期几
#include <cstdio>
#include <cstring>

int month[13][2]={
    {0,0},{31,31},{28,29},{31,31},{30,30},{31,31},{30,30},{31,31},{31,31},
    {30,30},{31,31},{30,30},{31,31}
};
char month_name[13][20]={
    "","January","February","March","April","May","June","July","August",
    "September","October","November","December"
};
char week_name[7][20]={
    "Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"
};
bool isLeap(int year){
    return (year%4==0&&year%100!=0)||(year%400==0);
}
int main(){
    int d,m,y;
    char s[20];
    while(scanf("%d%s%d",&d,s,&y)!=EOF){
        for(m=1;m<=12;m++){
            if(strcmp(s,month_name[m])==0) break;
        }
        int y1=1,m1=1,d1=1,day=1;
        while(y1<y||m1<m||d1<d){
            d1++;
            if(d1==month[m1][isLeap(y1)]+1){
                d1=1;
                m1++;
            }
            if(m1==13){
                m1=1;
                y1++;
            }
            day++;
        }
        printf("%s\n",week_name[day%7]);
    }
    return 0;
}

#include <stdio.h>
#include <string.h>
using namespace std;
int test(int year)
{
    if(year%400==0||(year%100!=0&&year%4==0))
        return 1;
    else
        return 0;
}
int main(void)
{
    string months[12]={"January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"};
    int day,year,month;
    int c,m,d,y,w;
    string str_m;
    while(cin>>day>>str_m>>year)
    {
        for(int i=0;i<12;i++)
        {
            if(str_m==months[i])
            {
                month=i+1;
                break;
            }
        }
        if(month==1)
        {
            m=13;
            y=year-1;
        }
        else if(month==2)
        {
            m=14;
            y=year-1;
        }
        else
        {
            m=month;
            y=year;
        }
        c=y/100;
        d=day;
        w = (d + 2*m + 3*(m + 1)/5 + y + y/4 - y/100 + y/400 + 1) % 7;
        switch(w){
            case 0:cout<<"Sunday"<<endl;break;
            case 1:cout<<"Monday"<<endl;break;
            case 2:cout<<"Tuesday"<<endl;break;
            case 3:cout<<"Wednesday"<<endl;break;
            case 4:cout<<"Thursday"<<endl;break;
            case 5:cout<<"Friday"<<endl;break;
            case 6:cout<<"Saturday"<<endl;break;
        }
    }
    return 0;
}

#include<iostream>
#include<stdio.h>
#include<string.h>
using namespace std;
char  mon[][20]={" ","January","February","March","April","May","June","July","August","September","October","November","December"};
char  week[][20]={"Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"};
int day[13]={0,31,28,31,30,31,30,31,31,30,31,30,31};
bool leap(int y){
  if(y%400==0||(y%4==0&&y%100!=0))return true;
  else return false;
}
int days(int y,int m,int d){
  int sum=0;
  for(int i=1;i<y;++i){
    if(leap(i))sum+=366;
    else sum+=365;
    }
  if(leap(y))day[2]=29;
  else day[2]=28;
  for(int j=1;j<m;++j){
    sum+=day[j];
  }
  sum+=d;
  return sum;
}
int main(){
  int y,m,d;
  char month[20];

  while(cin>>d>>month>>y){
    for(int i=1;i<13;++i){

        if(strcmp(month,mon[i])==0){
           m=i;
           break;
        }
    }
    int cnt1=days(y,m,d);
    int cnt2=days(2018,3,7);
    int del=cnt1-cnt2;
    del=del%7;
    cout<<week[(del+3)%7];
  }
  return 0;
}

	

#include<stdio.h>
#include<string.h>
#define ISYEAR(x) x%100!=0&&x%4==0||x%400==0?1:0
int dateOfMonth[13][2]={
    0,0,
    31,31,
    28,29,
    31,31,
    30,30,
    31,31,
    30,30,
    31,31,
    31,31,
    30,30,
    31,31,
    30,30,
    31,31
};
struct Date{
    int Year;
    int Month;
    int Day;
    void NextDay(){
        Day++;
        if(Day>dateOfMonth[Month][ISYEAR(Year)]){
            Day=1;
            Month++;
            if(Month>12){
                Month=1;
                Year++;
            }
        }
    }
};
int buf[3001][13][32];
char MonthName[13][20]={
    " ",
    "January",
    "February",
    "March",
    "April",
    "May",
    "June",
    "July",
    "August",
    "September",
    "October",
    "November",
    "December"
};
char WeekName[7][20]={
    "Sunday", 
    "Monday",
    "Tuesday",
    "Wednesday",
    "Thursday",
    "Friday",
    "Saturday"
};
int main(){
    Date tmp;
    tmp.Year=0;
    tmp.Month=1;
    tmp.Day=1;
    int cnt=0;
    while(tmp.Year!=3001){
        buf[tmp.Year][tmp.Month][tmp.Day]=cnt;
        tmp.NextDay();
        cnt++;
    }
    int d,m,y;
    char s[20];
    while(scanf("%d%s%d",&d,s,&y)!=EOF){
        for(m=1;m<13;m++){
            if(strcmp(MonthName[m],s)==0)
                break;
        }
    }
    int days=(buf[y][m][d]-buf[2012][7][16])+1;
    printf("%s",WeekName[(days%7+7)%7]);    
}

//王道机试指南解法
#include<iostream>
#include<cstring>
#define ISLEAP(x)  (x%4==0&&x%100!=0)||x%400==0?1:0
int YofM[13][2] = {
    0,0,31,31,28,29,31,31,30,30,31,31,30,30,
    31,31,31,31,30,30,31,31,30,30,31,31
};
struct Data {
    int data;
    int month;
    int year;
    Data() {
        data = 1; month = 0; year = 0;
    }
    void nextdata() {
        data++;
        if (data>YofM[month][ISLEAP(year)]) {
            month++; data = 1;
            if (month>12)
            {
                year++; month = 1;
            }
        }//if
    }
};
char monthName[13][20] = {
    "","January","February","March","April","May","June","July",
    "August","September","October","November","December"
};
char weekName[7][20] = {
    "Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"
};
int Daycount[3001][13][32];
int main() {
    Data D;
    int num = 0;
    while (D.year <= 3000) {
        Daycount[D.year][D.month][D.data] = num;
        D.nextdata();
        num++;
    }//while
    int d, m, y;
    char s[20];
    while (std::cin >> d >> s >> y) {
        for (m = 1; m<13; m++) {
            if (strcmp(s, monthName[m]) == 0) { break; }
        }//for
        int i = Daycount[y][m][d] - Daycount[2018][2][25];
        std::cout << weekName[(i % 7 + 7) % 7];
    }//while
    return 0;
}

from datetime import datetime
Month = {'May': 5, 'December': 12, 'October': 10, 'August': 8,
         'July': 7, 'February': 2, 'January': 1, 'September': 9,
         'March': 3, 'April': 4, 'November': 11, 'June': 6}
try:
    while 1:
        k = raw_input().split()
        print datetime(int(k[2]),Month[k[1]],int(k[0])).strftime('%A').capitalize()
except:
    pass

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#define IFYEAP(x) x%100!=0 && x%4==0 || x%400==0 ? 1:0
int yearDay[13][2] = {
    0, 0,
    31, 31,
    28, 29,
    31, 31,
    30, 30,
    31, 31,
    30, 30,
    31, 31,
    31, 31,
    30, 30,
    31, 31,
    30, 30,
    31, 31
};

char weekInfo[7][10] = {"Monday",
"Tuesday", "Wednesday",
"Thursday", "Friday", "Saturday", "Sunday" };

char monthInfo[13][20] = { "0",
"January", "February",
"March", "April",
"May", "June",
"July", "August",
"September", "October",
"November", "December" };

int todayIndex = 2;
typedef struct dateInfo {
    int day;
    int month;
    int year;
    void nextDate() {
        day++;
        if (day > yearDay[month][IFYEAP(year)]) {
            month++;
            day = 1;
            if (month > 12) {
                month = 1;
                year++;
            }
        }
    }
}DateInfo;

int main() {
    int d2;
    char *m2_char = (char*)malloc(sizeof(char) * 10);
    int y2;
    scanf("%d%s%d", &d2, m2_char, &y2);
    int m2;
    for (int i = 0; i<13; i++) {
        if (!strcmp(m2_char, monthInfo[i])) {
            m2 = i;
        }
    }
    DateInfo date2, date1;
    date2.day = d2;
    date2.month = m2;
    date2.year = y2;
    date1.day = 31;
    date1.month = 7;
    date1.year = 2019;
    int index = -1;
    if (date1.year > date2.year) index = 2;
    else if (date1.year < date2.year) index = 1;
    else {
        if (date1.month > date2.month) index = 2;
        else if (date1.month < date2.month) index = 1;
        else {
            if (date1.day > date2.day) index = 2;
            else if (date1.day < date2.day) index = 1;
        }
    }
    switch (index) {
    case -1: break;
    case 1:
        while (date1.year != date2.year || date1.month != date2.month || date1.day != date2.day) {
            date1.nextDate();
            todayIndex = (todayIndex + 1) % 7;
        }
        break;
    case 2:
        while (date1.year != date2.year || date1.month != date2.month || date1.day != date2.day) {
            date2.nextDate();
            todayIndex = (todayIndex + 1) % 7;
        }
        break;
    }
    printf("%s", weekInfo[todayIndex]);
}

#include<bits/stdc++.h>
using namespace std;
int main()
{
    string MONTH[13] = {"","January", "February", "March", "April","May", "June", "July", "August","September","October","November","December"};
    string WEEKDAY[8] ={"","Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday","Sunday"};
    map<string,int>map1;
    map<int,string>map2;
    for(int i=1;i<8;i++)
        map2[i] = WEEKDAY[i];
    for(int i=1;i<13;i++)
        map1[MONTH[i]] = i ;
    int day,year;
    string month;
    while(cin>>day>>month>>year)
    {
        int mon = map1[month];
        if(mon==1||mon==2)
        {
            mon+=12;
            year-=1;
        }
        int res = (day+2*mon+3*(mon+1)/5+year+year/4-year/100+year/400)%7 + 1;
        cout<<map2[res]<<endl;
    }
    return 0;
}

基姆拉尔森计算公式
W= (d+2*m+3*(m+1)/5+y+y/4-y/100+y/400) mod 7

在公式中d表示日期中的日数，m表示月份数，y表示年数。

#include<stdio.h>
#include<string.h>
int month[13][2] =
{
    {0,0},//0
    {31,31},//1
    {28,29},//2
    {31,31},//3
    {30,30},//4
    {31,31},//5
    {30,30},//6
    {31,31},//7
    {31,31},//8
    {30,30},//9
    {31,31},//10
    {30,30},//11
    {31,31}//12
};
int isR(int n)
{
    if(n%4==0&&n%100!=0||n%400==0)
        return 1;
    return 0;
}
int main()
{
    char mon[13][100] = {"","January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"};
    char week[8][100] = {"","Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"};
    int y,d,m,w;
    char temp[100];
    while(scanf("%d %s %d",&d, temp, &y)!=EOF)
    {
        int y0 = 2001, m0 = 10, d0 = 9, w0 = 3;
        for(int i=1; i<13; i++)
        {
            if(strcmp(temp,mon[i])==0)
            {
                m = i;
                break;
            }
        }
        int flag = 0;
        while(y0 < y || m0 < m || d0 < d)
        {
            flag = 1;
            d0++;
            w0++;
            if(d0==month[m0][isR(y0)]+1)
            {
                d0 = 1;
                m0++;
            }
            if(m0==13)
            {
                y0++;
                m0 = 1;
            }
            if(w0==8)
                w0 = 1;
        }
        if(flag==1 || y==y0&&m==m0&&d==d0)
        {    flag = 1;
            printf("%s\n", week[w0]);
        }
    
        while(y < y0 || m < m0 || d < d0)
        {
             d++;
             w0--;
             if(d==month[m][isR(y)]+1)
             {
                d=1;
                m++;
            }
            if(m==13)
            {
                m=1;
                y++;
            }
            if(w0==0)
                w0 = 7;
        }
        if(flag==0)
            printf("%s\n", week[w0]);
        
    }

}

#include<cstdio>
#include<string>
#include<iostream>

using namespace std;

// 2019.01.01 Tuesday

const int dayOfMonth[12] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
const string date[7] = {"Tuesday", "Wednesday", "Thursday", "Friday", 
                        "Saturday", "Sunday", "Monday"};

bool isLeapYear(int n) {
    if (n % 4 == 0) {
        if (n % 100) {
            return true;
        } else {
            if (n % 400) {
                return false;
            } else {
                return true;
            }
        }
    }
    return false;
}

int main() {
    int day = 0, year = 0;
    char month[10];
    while (~scanf("%d %s %d", &day, month, &year)) {
        int days = 0;
        bool beforeFeb = false;
        int monthNum = 0;
        switch (month[0]) {
            case 'J':
                if (month[1] == 'a') {
                    monthNum = 1;
                } else if (month[2] == 'n') {
                    monthNum = 6;
                } else {
                    monthNum = 7;
                }
                break;
            case 'F':
                monthNum = 2;
                break;
            case 'M':
                if (month[2] == 'r') {
                    monthNum = 3;
                } else {
                    monthNum = 5;
                }
                break;
            case 'A':
                if (month[1] == 'p') {
                    monthNum = 4;
                } else {
                    monthNum = 8;
                }
                break; 
            case 'S':
                monthNum = 9;
                break;
            case 'O':
                monthNum = 10;
                break;
            case 'N':
                monthNum = 11;
                break;
            default:
                monthNum = 12;
        }
        beforeFeb = monthNum <= 2;
        if (year < 2019) {
            days += (2019 - year - 1) * 365;
            for (int i = year + 1; i < 2019; ++i) {
                if (isLeapYear(i)) {
                    ++days;
                }
            }
            for (int i = monthNum; i < 12; ++i) {
                days += dayOfMonth[i];
            }
            days += dayOfMonth[monthNum - 1] - day + 1;
            if (beforeFeb && isLeapYear(year)) {
                ++days;
            }
        } else {
            days += (year - 2019) * 365;
            for (int i = 2019; i < year; ++i) {
                if (isLeapYear(i)) {
                    ++days;
                }
            }
            for (int i = 0; i < monthNum - 1; ++i) {
                days += dayOfMonth[i];
            }
            days += day;
            if (!beforeFeb && isLeapYear(year)) {
                ++days;
            }
        }
        --days;
        cout << date[days % 7] << endl;
    }
    return 0;
}

#include <cstdio>
#include <string>
#include <map>
#include <iostream>
using namespace std;
string monthName[13]={"December", "January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"};
string weekName[8]={"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"};
map<string,int> monthNum;
map<string,int> weekNum;
int notleapDays[13]={31,31,28,31,30,31,30,31,31,30,31,30,31};
int leapDays[13]={31,31,29,31,30,31,30,31,31,30,31,30,31};
struct Date
{
    int year,month,day,week;
};
void init()
{
    for(int i=1;i<=12;i++)
        monthNum[monthName[i]]=i;
    for(int i=1;i<=7;i++)
        weekNum[weekName[i]]=i;
}
bool isLeap(int year)
{
    if((year%4==0&&year%100!=0)||year%400==0)
        return true;
    return false;
}
//-1:calday是未来 0:calday是今天 1:calday是过去 
int compare(Date today,Date calday)
{
    if(today.year<calday.year)
        return -1;
    else if(today.year>calday.year)
        return 1;
    else
    {
        if(today.month<calday.month)
            return -1;
        else if(today.month>calday.month)
            return 1;
        else
        {
            if(today.day<calday.day)
                return -1;
            else if(today.day>calday.day)
                return 1;
            else
                return 0;
        }
    }
}
//calday是过去
int getWeek1(Date today,Date calday)
{
    while(today.day!=calday.day||today.month!=calday.month||today.year!=calday.year)
    {
        today.day--;
        if(today.day==0)
        {
            today.month--;
            if(today.month==0)
            {
                today.month=12;
                today.year--;
            }
            if(isLeap(today.year)==true)
                today.day=leapDays[today.month];
            else
                today.day=notleapDays[today.month];
        }
        today.week--;
        if(today.week==0)
            today.week=7;
    }
    return today.week;
}
//calday是未来
int getWeek2(Date today,Date calday)
{
    while(today.day!=calday.day||today.month!=calday.month||today.year!=calday.year)
    {
        today.day++;
        if((isLeap(today.year)==true&&today.day>leapDays[today.month])
            ||(isLeap(today.year)==false&&today.day>notleapDays[today.month]))
        {
            today.day=1;
            today.month++;
            if(today.month==13)
            {
                today.month=1;
                today.year++;
            }
        }
        today.week++;
        if(today.week==8)
            today.week=1;
    }
    return today.week;
}
int main()
{
    init();
    Date today,calday;
    today.day=7;today.month=3;today.year=2019;today.week=4;
    while(scanf("%d",&calday.day)!=EOF)
    {
        string str;
        cin>>str;
        calday.month=monthNum[str];
        scanf("%d",&calday.year);
        if(compare(today,calday)==1)
            //calday是过去
            calday.week=getWeek1(today,calday);
        else if(compare(today,calday)==-1)
            //calday是未来
            calday.week=getWeek2(today,calday);
        else
            calday.week=today.week;
        cout<<weekName[calday.week]<<endl;
    }
    return 0;
}

#include <stdio.h>
#include <string.h>
#define leapyear(x) x%100!=0&&x%4==0||x%400==0? 1:0
#define today 1    //运行当天是周几
int dayOfMonth[13][2]={0,0,31,31,28,29,31,31,30,30,31,31,30,30,31,31,31,31,30,30,31,31,30,30,31,31};
int buf[3001][13][32];
char weekname[7][10]={"Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"};
char monthname[13][10]={"","January","February","March","April","May","June","July","August","September","October","November","December"};

typedef struct Date{
    int year;
    int month;
    int day;
    void nextDay(){
        day++;
        if(day>dayOfMonth[month][leapyear(year)]){
            day=1;
            month++;
            if(month>12){
                month=1;
                year++;
            }
        }
    }
};
int main(){
    Date init;
    int d=0;        //日期差
    init.day=1;
    init.month=1;
    init.year=0;
    while(init.year!=3001){
        buf[init.year][init.month][init.day]=d;
        init.nextDay();
        d++;
    }
    int year,day;
    char s[10];
    while(scanf("%d %s %d",&day,s,&year)!=EOF){
        int month;
        for(month=1;month<=12;month++){
            if(strcmp(monthname[month],s)==0) break;
        }
        int d1=buf[2019][2][25];        //今天离初始日期差
        int d2=buf[year][month][day];        //目标日期离初始日期差
        int index;
        if(d1>d2){
            int k=(d1-d2)%7;            //今天比目标日期后，往前推算星期几
            index=(today-k+7)%7;
        }else {
            int k=(d2-d1)%7;
            index=(today+k+7)%7;
        }
        printf("%s\n",weekname[index]);
    }
    return 0;
}

参考别人的代码，Scanner改为BufferedReader，if改为HashMap，时间快了三分之一（21ms）

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class Main {
    static String[] week = new String[] { 
            "Sunday", "Monday", "Tuesday", "Wednesday", 
            "Thursday", "Friday", "Saturday" };
    static int[] dayOfMonth = new int[] { 31, 0, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
    static List<Integer> dayOfYear = new ArrayList<>();
    static Map<String, Integer> monthMap = new HashMap<>();
    static {
        monthMap.put("January", 1);
        monthMap.put("February", 2);
        monthMap.put("March", 3);
        monthMap.put("April", 4);
        monthMap.put("May", 5);
        monthMap.put("June", 6);
        monthMap.put("July", 7);
        monthMap.put("August", 8);
        monthMap.put("September", 9);
        monthMap.put("October", 10);
        monthMap.put("November", 11);
        monthMap.put("December", 12);
    }

    public static void main(String[] args) throws IOException {
        dayOfYear.add(365);
        int today = getTotalDayCount(2019, 2, 24);

        String line;
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        while ( (line=reader.readLine()) != null ) {
            String[] param = line.split(" ");
            int day = Integer.parseInt(param[0]);
            int month = monthMap.get(param[1]);
            int year = Integer.parseInt(param[2]);
            int curDay = getTotalDayCount(year, month, day);

            if (today >= curDay) {
                System.out.println(week[(7 - (today - curDay) % 7) % 7]);
            } else {
                System.out.println(week[(curDay - today) % 7]);
            }
        }
        reader.close();
    }

    static int getTotalDayCount(int year, int month, int day) {
        for (int i = dayOfYear.size(); i < year; i++) {
            dayOfYear.add(dayOfYear.get(i - 1) + getDayCount(i));
        }
        int curDayCount = dayOfYear.get(year - 1);
        for (int i = 0; i < month - 1; i++) {
            curDayCount += dayOfMonth[i];
            if (i == 1) {
                if (isLeap(year)) {
                    curDayCount += 29;
                } else {
                    curDayCount += 28;
                }
            }
        }
        curDayCount += day;
        return curDayCount;
    }

    static boolean isLeap(int year) {
        return (year % 4 == 0 && year % 100 != 0) || year % 400 == 0;
    }

    static int getDayCount(int year) {
        if (isLeap(year)) return 366;
        return 365;
    }
}

#include<stdio.h>
#include<string.h>
using namespace std;
#define ISYEAP(x) x%100!=0&&x%4==0 || x%400==0 ?1:0
int dayOfMonth[13][2]={
 0,0,
 31,31,
 28,29,
 31,31,
 30,30,
 31,31,
 30,30,
 31,31,
 31,31,
 30,30,
 31,31,
 30,30,
 31,31
};
struct Date{
 int day;
 int month;
 int year;
 void nextDay(){
  day++;
  if(day>dayOfMonth[month][ISYEAP(year)]){
   day=1;
   month++;
   if(month>12){
    month=1;
    year++;
   }
  } 
 }
}; 
int buf[5001][13][32];
char month[13][20]={"","January", "February", "March", "April", "May", "June", "July", "August", "September", 
      "October", "November", "December"};
char week[7][20]={"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"};
int main(){
 Date tmp;
 tmp.day=1;
 tmp.month=1;
 tmp.year=0;
 int idx=1;
 while(tmp.year!=5001){
  buf[tmp.year][tmp.month][tmp.day]=idx++;
  tmp.nextDay();
 }
 int d,y;
 char s[20];
 while(~scanf("%d%s%d",&d,s,&y)){
  int m;//记录month 
  for(m=1;m<=12;m++){
   if(strcmp(month[m],s)==0)
    break;
  }
  int days=buf[y][m][d]-buf[2019][2][21]+4;
  puts(week[(days%7+7)%7]);
 }
 return 0;
}

• 自行判断闰年，然后以2月的一个星期日为基准天数，进行计算

  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.List;
  import java.util.Scanner;
  public class DayOfWeek {
  
    private static int[] times = {
            31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
    };
    private static String[] months = {
            "January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"
    };
    private static String[] days = {
            "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"
    };
  
    public static void main(String[] args) {
        List<String> inList = new ArrayList<String>();
        String in;
        Scanner sc = new Scanner(System.in);
        while (sc.hasNextLine()) {
            in = sc.nextLine();
            if (in.equals("")) {
                break;
            }
            inList.add(in);
        }
  
        for (String res :
                inList) {
            String[] strs = res.split(" ");
            int day = Integer.parseInt(strs[0]);
            int month = Arrays.asList(months).indexOf(strs[1]) + 1;
            int year = Integer.parseInt(strs[2]);
            OwnDate date = new OwnDate(year, month, day);
            OwnDate flagDate = new OwnDate(2019, 2, 24);
            int diff;
            boolean fl = flag(date, flagDate);
            if (fl) {
                diff = (getValue(date, flagDate) - 1) % 7;
            } else {
                diff = (getValue(flagDate, date) - 1) % 7;
            }
  //            int diff = (getValue(date, new OwnDate(2001, 10, 14)) - 1) % 7;
            if (fl) {
                System.out.println(days[7 - diff]);
            } else {
                System.out.println(days[diff]);
            }
        }
  
    }
  
    private static class OwnDate {
        int year;
        int month;
        int day;
  
        public OwnDate(int year, int month, int day) {
            this.year = year;
            this.month = month;
            this.day = day;
        }
  
        public OwnDate() {
        } 
    }
  
    private static boolean isFlag(int year) {
        return (year % 4 == 0 && year % 100 != 0 || year % 100 == 0 && year % 400 == 0);
    }
  
    private static int getValue(OwnDate date1, OwnDate date2) {
        int res = 1;
        int diff = 0;
        int i;
        for (i = date1.year; i < date2.year; i++) {
            res += isFlag(i) ? 366 : 365;
        }
  
        if (date1.month < date2.month) {
            for (int j = date1.month - 1; j < date2.month - 1; j++) {
                diff += times[j];
                if (isFlag(i) && j == 1) {
                    diff++;
                }
            }
            res += diff;
        } else if (date1.month > date2.month) {
            for (int j = date2.month - 1; j < date1.month - 1; j++) {
                diff += times[j];
                if (isFlag(i) && j == 1) {
                    diff++;
                }
            }
            res -= diff;
        }
  
        res += (date2.day - date1.day);
  
        return res;
    }
  
    private static boolean flag(OwnDate date1, OwnDate date2) {
        boolean flag = false;
        if (date1.year < date2.year) {
            flag = true;
        } else if (date1.year == date2.year) {
            if (date1.month < date2.month) {
                flag = true;
            } else if (date1.month == date2.month) {
                if (date1.day < date2.day) {
                    flag = true;
                }
            }
        }
        return flag;
    }
  }