十分奇怪的错误方式

#include<bits/stdc++.h>
using namespace std;
map<long long,int>mp;
long long a[1000005],sum[1000005];
int main(){
//	freopen("trip5.in","r",stdin);
//	freopen("trip5.out","w",stdout); 
    int t;
    scanf("%d",&t);
    while(t--){
        int maxn=0;
        memset(sum,0,sizeof sum);
        int n;
        scanf("%d",&n);
        for(int i=1;i<=n;i++){
            scanf("%lld",a+i);
            sum[i]=sum[i-1]+a[i];
            mp[sum[i]]++;
        }
        long long t=0;
        for(int i=0;i<=n;i++){
            // cout<<t<<endl;
            maxn=max(maxn,mp[t]);
            t=sum[i];
            mp[sum[i]]--;
        }
        printf("%d\n",maxn);
    }
    return 0;
}