为什么给数列排序会WA？实在想不明白了

#include<bits/stdc++.h>
using namespace std;
int main()
{
    int _;cin >> _;
    while (_--)
    {
        int n,ans=0;
        int a[110] = {0};
        cin >> n;

        for (int i = 1; i <= n; i++)
            cin >> a[i];

       // sort(a + 1, a + 1 + n);

        for (int i = 1; i <= n; i++)
        {
            for (int j = i; j <= n; j++)
            {
                for (int k = j; k <= n; k++)
                {
                    if (a[i] + a[j] == a[k])
                        ans++;
                }
            }
        }
        cout << ans << endl;
    }
    
    return 0;
}