CF1400D Zigzags（刻骨铭心的失误，又一次上分失败）

#include<bits/stdc++.h>
using namespace std;
const int maxn=3005;
typedef long long ll;
int t;
int a[maxn];
ll c[maxn][maxn];
int n;
int main () {
    int t;
    scanf("%d",&t);
    while (t--) {
        scanf("%d",&n);
        for (int i=0;i<=n;i++)
            for (int j=0;j<=n;j++)    
                c[i][j]=0;
        for (int i=1;i<=n;i++) scanf("%d",a+i);
        for (int i=1;i<=n;i++) {
            for (int j=1;j<=n;j++) {
                if (j==a[i])
                    c[i][j]=c[i-1][j]+1;
                else
                    c[i][j]=c[i-1][j];
            }
        } 
        ll ans=0;
        for (int i=1;i<=n;i++) {
            for (int j=i+1;j<=n;j++) {
                ans+=(c[i-1][a[j]]-c[0][a[j]])*(c[n][a[i]]-c[j][a[i]]);
            } 
        }
        printf("%lld\n",ans);
    }
}