【二分图+最大匹配】北大 poj 3041 Asteroids

/* THE PROGRAM IS MADE BY PYY */ /*----------------------------------------------------------------------------// Copyright (c) 2011 panyanyany All rights reserved. URL : http://poj.org/problem?id=3041 Name : 3041 Asteroids Date : Saturday, November 19, 2011 Time Stage : one hour Result: 9578655 panyanyany 3041 Accepted 224K 32MS C++ 1259B 2011-11-19 21:21:01 9578476 panyanyany 3041 Accepted 264K 16MS C++ 1304B 2011-11-19 20:46:42 9578453 panyanyany 3041 Wrong Answer C++ 1310B 2011-11-19 20:42:34 Test Data : Review : 一开始觉得是最小顶点覆盖，结果错了，看人家的钥匙报告，才知道原来是 最大匹配……囧…… //----------------------------------------------------------------------------*/ #include <stdio.h> #include <string.h> #include <vector> using std::vector ; #define MAXSIZE 508 int n, k ; int link[MAXSIZE], cover[MAXSIZE] ; vector<int> adj[MAXSIZE] ; int find (int cur) { int i, j ; for (i = 0 ; i < adj[cur].size () ; ++i) { j = adj[cur][i] ; if (cover[j] == false) { cover[j] = true ; if (link[j] == false || find (link[j])) { link[j] = cur ; return 1 ; } } } return 0 ; } int main () { int i, j ; int r, c ; int sum ; while (~scanf ("%d%d", &n, &k)) { for (i = 1 ; i <= n ; ++i) adj[i].clear () ; for (i = 1 ; i <= k ; ++i) { scanf ("%d%d", &r, &c) ; adj[r].push_back (c) ; } memset (link, 0, sizeof (link)) ; sum = 0 ; for (i = 1 ; i <= n ; ++i) { memset (cover, 0, sizeof (cover)) ; sum += find (i) ; } // 感觉应该是最小顶点覆盖，怎么会是最大匹配呢？ printf ("%d\n", sum) ; } return 0 ; }