题解 | 喜欢切数组的红

#include <iostream>
#include <vector>
using namespace std;

int main() {
    int n;
    cin>>n;
    vector<long long> qzh(n),zs(n,0);
    cin>>qzh[0];
    if(qzh[0]>0)zs[0]=1;
    for(int i=1;i<n;i++){
        long long a;
        cin>>a;
        qzh[i]=qzh[i-1]+a;
        if(a>0)zs[i]=zs[i-1]+1;
        else zs[i]=zs[i-1];
    }
    long long sum=qzh.back();
    if(sum%3!=0){
        cout<<0;
        return 0;
    }
    sum/=3;
    int num=0;
    vector<int> ii,jj;
    for(int i=0;i<n;i++){
        if(qzh[i]==sum){
            ii.push_back(i);
        }else if(qzh[i]==2*sum){
            jj.push_back(i);
        }
    }
    for(int i:ii){
        for(int j:jj){
            if(i<j&&zs[i]>0&&zs[j]-zs[i]>0&&zs[n-1]-zs[j]>0)num++;
        }
    }
    cout<<num;
}