美团笔试编程第二题 - 整除7

定义如下结构体
/*
MyNum{
num
*mod7 = num %7;
preFactor = 10^x; ( 10^(x-1) <= num < 10^x)
premod = preFactor %7;
*needAppendTime ;(needAppendTime * premod + mod7)%7 = 0;
}
*/
class MyNum {
public int mod7;
public int needAppendTime;
}
举例分析,对于用例a=1997,b=127;因为127.mod=1,在127填加的数,需要扩大127.preFactor=1000倍,而每增加1000,mod(1000 + 127) = mod( mod(1000 * 1) + mod(127) ) = mod(6 + 1) = 0;所以需要 a.mod = 1。则1997127 % 7 = 0;
========================
127 1996 12
mod     1    1    5
factor  1000 10000 100
fMod    6    4    2
time    1    5    1
则mod = time;
1996-127;  12-1996; 127-12; 1996-12

import java.util.*;
import java.lang.*;

/*
3
127 1996 12

4
 */
public class MeiTuanA {
    public static final int MOD = 7;
    public static int getCnt(int[] sumRest, MyNum node) {
        int ansCnt = sumRest[node.needAppendTime];
        if (node.mod7 == node.needAppendTime) {
            ansCnt--;
        }
        return ansCnt;
    }

    public static int solution(int n, int[] nums) {
        MyNum[] nodes = new MyNum[n];
        int[] sumRest = new int[MOD];

        for (int i = 0; i < n; i++) {
            int curNum = nums[i];
            int mod7 = curNum % 7;

            int pows = (int)(Math.log(nums[i]) / Math.log(10) );
            int preFactor = (int) Math.pow(10, pows + 1);
            int preFMode7 = preFactor % 7;
            int needTime = 0;
            while( ( needTime * preFMode7 + mod7) % 7 != 0 ) {
                needTime++;
            }
            nodes[i] = new MyNum(mod7, needTime);
            sumRest[mod7]++;
        }

        int cnt = 0;
        for (int i = 0; i < n; i++) {
            MyNum curNum = nodes[i];
            cnt += getCnt(sumRest, curNum);
        }
        return cnt;
    }

    public static void main(String[] args) {
        Scanner cin = new Scanner(System.in);
        int n = cin.nextInt();
        int[] nums = new int[n];
        for (int i = 0; i < n; i++) {
            nums[i] = cin.nextInt();
        }
        System.out.println( solution(n, nums) );
    }
}

class MyNum {
    public int mod7;
    public int needAppendTime;

    public MyNum(int mod7, int needAppendTime) {
        this.mod7 = mod7;
        this.needAppendTime = needAppendTime;
    }
}


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