POJ 3692 Kindergarten

题目链接

题意：一个班级内，男的都互相认识，女的都互相认识，现在有k对男女互相认识，要求选出最多的人，使得他们两两互相认识

思路：最大独立集，把不认识的连边，就可以求出最大独立集就是两两互相认识的

代码：

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

const int N = 205;

int G, B, k, graph[N][N];
vector<int> g[N];

int left[N], vis[N];

bool dfs(int u) {
	for (int i = 0; i < g[u].size(); i++) {
		int v = g[u][i];
		if (vis[v]) continue;
		vis[v] = 1;
		if (!left[v] || dfs(left[v])) {
			left[v] = u;
			return true;
		}
	}
	return false;
}

int hungary() {
	int ans = 0;
	memset(left, 0, sizeof(left));
	for (int i = 1; i <= G; i++) {
		memset(vis, 0, sizeof(vis));
		if (dfs(i)) ans++;
	}
	return ans;
}

int main() {
	int cas = 0;
	while (~scanf("%d%d%d", &G, &B, &k) && G) {
		int u, v;
		memset(graph, 0, sizeof(graph));
		while (k--) {
			scanf("%d%d", &u, &v);
			graph[u][v] = 1;
		}
		for (int i = 1; i <= G; i++) {
			g[i].clear();
			for (int j = 1; j <= B; j++) {
				if (graph[i][j]) continue;
				g[i].push_back(j);
			}
		}
		printf("Case %d: %d\n", ++cas, G + B - hungary());
	}
	return 0;
}