51nod 1267 4个数和为0

#include <algorithm>
#include <cstdlib> 
#include <cstdio>
#define mo 20047
#define mo2 13831

using namespace std;

struct node
{
    int x,y,z;
    bool operator<(node a)const
    {
        return z<a.z;
    }
}h[1000001];
int A[1001],cnt,n;
int main()
{
    scanf("%d",&n);
    if(n<3) {printf("No");return 0;} 
    for(int i=1;i<=n;i++) {scanf("%d",&A[i]);}
    for(int i=1;i<=n;i++)
    {
        for(int j=i+1;j<=n;j++)
        {
            h[++cnt].x=A[i];
            h[cnt].y=A[j];
            h[cnt].z=A[i]+A[j];
        }
    }
    sort(h+1,h+1+cnt);
    int l=1,r=cnt;
    while(l<r-1)
    {
        int mid=(l+r)>>1;
        if(h[l].z+h[r].z==0&&h[l].x!=h[l].y&&h[r].x!=h[l].x&&h[r].y!=h[l].y&&h[l].x!=h[r].y&&h[l].y!=h[r].x)
            {printf("Yes");return 0;}
        if(h[l].z+h[r].z>0) r--; 
        else if(h[l].z+h[mid].z<0) l++;
        else if(h[l].z+h[mid].z) break;
    }
    printf("No");
    return 0;
}