【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=, r=n-, mid;

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

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

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

     return ;
 }