POJ 2785 4 Values whose Sum is 0 二分

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const int maxn=4100;
const int maxm=10000;
int n,m;
int a[4][maxn];
int b[maxn*maxn];
int main(){
	while (~scanf("%d",&n)){
        for (int i=0;i<n;i++){
            for (int k=0;k<4;k++){
                scanf("%d",&a[k][i]);
            }
        }
        for (int i=0;i<n;i++){
            for (int j=0;j<n;j++){
                b[i*n+j]=a[0][i]+a[1][j];
            }
        }
        m=n*n;
        sort(b,b+m);
        int ans=0;
        for (int i=0;i<n;i++){
            for (int j=0;j<n;j++){
                int t=a[2][i]+a[3][j];
                int l=lower_bound(b,b+m,-t)-b;
                int r=upper_bound(b,b+m,-t)-b;
                ans+=r-l;
            }
        }
        printf("%d
",ans);
	}
	return 0;
}

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