我无法正确运行所有测试用例，怎么了？

Question

Complete the divisibleSumPairs function in the editor below. It should return the integer count of pairs meeting the criteria.

divisibleSumPairs has the following parameter(s):

• n : the integer length of array ar

• ar : an array of integers

• k : the integer to divide the pair sum by

Print the number of (i, j) pairs where i < j and ar[i] + ar[j] is evenly divisible by k .

I don't know what is wrong, only some cases has worked

  static int divisibleSumPairs(int n, int k, int[] ar) {
    int count = 0;
    for (int i=0; i<n; i++){
        for (int j=0; j<n; j++){
            if ((ar[i]<ar[j]) && ((ar[i]+ar[j])%k)== 0){
                count++;
            }
        }
    }
        return count;
}

Answer 1

The main problem is that you check for ar[i] < ar[j] while the problem statement says i < j :

static int divisibleSumPairs(int n, int k, int[] ar) {
    int count = 0;
    for (int i = 0; i < n; i++){
        for (int j = 0; j < n; j++){
            if (i < j && (ar[i] + ar[j]) % k == 0) {
                count++;
            }
        }
    }
    return count;
}

The algorithm can be further optimized to:

static int divisibleSumPairs(int n, int k, int[] ar) {
    int count = 0;
    for (int i = 0; i < n; i++){
        for (int j = i + 1; j < n; j++){
            if ((ar[i] + ar[j]) % k == 0) {
                count++;
            }
        }
    }
    return count;
}