京东8月6日Java开发笔试
1.数组求和
#京东##Java工程师#
package Test.Jd2;
import java.util.Scanner;
public class jd1 {
public static void main(String[] args){
Scanner in = new Scanner(System.in);
int n = in.nextInt();
double sum = 0;
for(double i = 1; i <= n; i++ ){
sum += (double) 1/((double)5 * ((double)2 * i - (double)1)) - (double)1/((double)5 * ((double)2 * i));
}
String result = String.format("%.4f", sum);
System.out.println(result);
}
}
2.回文素数
package Test.Jd2;
import java.util.Scanner;
public class jd2 {
public static void main(String[] args){
Scanner in = new Scanner(System.in);
int m = in.nextInt();
int n = in.nextInt();
int count = 0;
for(int i = m; i <= n; i++){
String s = String.valueOf(i);
for(int j = s.length() - 1; j >= 0; j--){
String temp = s.substring(0,j) + s.substring(j+1,s.length());
int a = Integer.parseInt(temp);
//System.out.println(a);
if(isPalindrome(a)){
if(isPrime(a)){
count++;
break;
}
}
}
}
System.out.println(count);
//System.out.println(isPrime(1));
}
public static boolean isPalindrome(int x) {
char[] chars=String.valueOf(x).toCharArray();
int left=0;
int right=chars.length-1;
while (left<=right){
if(chars[left++]!=chars[right--]){
return false;
}
}
return true;
}
//判断是不是素数
public static boolean isPrime(int x) {
int i = 2;
for(;i<x;i++) {
if (x % i == 0) {
break;
}
}
if(x == i){
return true;
}
return false;
}
}

查看7道真题和解析