【HDOJ】2428 Stars

先排序后二分。

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;

#define MAXN 1005

typedef struct {
    int x, y;
} node_st;

node_st nodes[MAXN];
int n;

bool comp(node_st a, node_st b) {
    if (a.x == b.x)
        return a.y < b.y;
    else
        return a.x < b.x;
}

bool find(int x, int y) {
    int l=0, r=n-1, mid;

    while (l <= r) {
        mid = (l+r)>>1;
        if (nodes[mid].x==x && nodes[mid].y==y)
            return true;
        if (nodes[mid].x > x)
            r = mid - 1;
        else if (nodes[mid].x < x)
            l = mid + 1;
        else if (nodes[mid].y > y)
            r = mid - 1;
        else
            l = mid + 1;
    }
    return false;
}

int main() {
    int t, ans;
    int i, j;

    scanf("%d", &t);
    while (t--) {
        scanf("%d", &n);
        for (i=0; i<n; ++i)
            scanf("%d%d", &nodes[i].x, &nodes[i].y);
        sort(nodes, nodes+n, comp);
        for (ans=0,i=0; i<n; ++i) {
            for (j=i+1; j<n; ++j) {
                if ((nodes[i].x-nodes[j].x)==(nodes[i].y-nodes[j].y) && find(nodes[i].x, nodes[j].y) && find(nodes[j].x, nodes[i].y))
                    ++ans;
            }
        }
        printf("%d
", ans);
    }

    return 0;
}