codeforce Number of Ways(暴力)

 #include<iostream>
 #include<cstdio>
 #include<cstring>
 #include<algorithm>
 #define N 500005
 using namespace std;
 typedef long long LL;
 LL prefix[N], suffix[N], num[N];
 LL cntSuf[N];
 int main(){
     int n;
     scanf("%d", &n);
     for(int i=; i<=n; ++i){
         scanf("%lld", &num[i]);
         prefix[i]=prefix[i-]+num[i];//前缀和
     }
     for(int i=n; i>=; --i)
         suffix[i]=suffix[i+]+num[i];//后缀和
     LL s=prefix[n]/;
     if(prefix[n]%!=){
         printf("0\n");
         return ;
     }
     LL ans=;
     for(int i=; i<=n; ++i)
         if(suffix[n-i+]==s) cntSuf[n-i+]=cntSuf[n-i+]+;
         else cntSuf[n-i+]=cntSuf[n-i+];
     for(int i=; i<=n; ++i)
         if(prefix[i]==s) ans+=cntSuf[i+];
     printf("%lld\n", ans);
     return ;
 }