C ++ Program Bug

Question

给定一个数组。程序应该找到所有对的总和可以除以7.我编写这段代码，但代码没有通过所有测试

#include <iostream>
using namespace std;

int m[7];

int main() {
     int n, k = 0;
     cin>>n;
     long long a;
     for(int i = 0; i < n; i++) {
          cin>>a;
          a %= 7;
          if(m[(7 - a) % 7] > 0) {
               k += m[(7 - a) % 7];
          }
          m[a]++;
     }
     cout<<k;
     return 0;
 }

Answer 1

我只是使用散列来存储余数的频率除以7：

int count7Divisibiles(int arr[], int n)
{
    // Create a frequency array to count 
    // occurrences of all remainders when 
    // divided by 7
    int freq[7] = {0, 0, 0, 0, 0, 0, 0};

    // Count occurrences of all remainders
    for (int i = 0; i < n; i++)
        ++freq[arr[i] % 7];

    // If both pairs are divisible by '7'
    int ans = freq[0] * (freq[0] - 1) / 2;


    // If one of them is equal
    // to 1 modulo 7 and the
    // other is equal to 3 
    // modulo 7
    ans += freq[1] * freq[6];

    // for 2%7 and 5%7
    ans += freq[2] * freq[5];

    //for 3%7 and 4%7
    ans += freq[3] * freq[4];

    return ans;
}

• 如果两者都可被7整除，则使用n*(n-1)/2
• 否则count(a%7)*count((7-a)%7)