poj 2785 4 Values whose Sum is 0

这道题，让我明白了lower_bound(),upper_bound()的威力啊

#include<iostream>#include<cstdio>#include<algorithm>using namespace std;int a[4003];int b[4003];int c[4003];int d[4003];int e[16000003];int main(){int n;cin>>n;int i;int j;for(i=0;i<n;i++)cin>>a[i]>>b[i]>>c[i]>>d[i];for(i=0;i<n;i++){for(j=0;j<n;j++)e[i*n+j]=a[i]+b[j];}sort(e,e+n*n);int   res;int sum=0;for(i=0;i<n;i++)for(j=0;j<n;j++){res=c[i]+d[j];sum+=upper_bound(e,e+n*n,-res)-lower_bound(e,e+n*n,-res);//返回个数，中间有几个相同的值也包含了，好巧妙}cout<<sum<<endl;}