二分图

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参考博客 by ling_wang
参考博客 by Matrix67

模板题 luogu3386

luogu3386 二分图匹配 の 传送门

这里是 匈牙利算法
Code

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

const int N = 1007, M = 1007;
int n, m, e, cnt, ans, nxt[N * M], to[N * M], head[N], ch[1010];
bool vis[1010];

inline int read(){
    int ans = 0, f = 1;
    char ch = getchar();
    while (ch < '0' || ch > '9'){
        if (ch == '-') f = -1;
        ch = getchar();
    }
    while (ch >= '0' && ch <= '9')
        ans = (ans << 3) + (ans << 1) + ch - 48, ch = getchar();
    return ans * f;
}
void add(int u, int v){
    nxt[++cnt] = head[u];
    to[cnt] = v;
    head[u] = cnt;
}
bool dfs(int k){
    for (int i = head[k]; i; i = nxt[i]){
        int v = to[i];
        if (!vis[v]){
            vis[v] = true;
            if (!ch[v] || dfs(ch[v])){
                ch[v] = k;
                return true;
            }	
        }
    }
    return false;
} 
int main(){
	//freopen("testdata.in.txt", "r", stdin);
    n = read(), m = read(), e = read();;
    for (int i = 1; i <= e; ++i){
        int x = read(), y = read();
        if (x <= n && y <= m)
            add(x, y);
    } 
    ans = 0;
    for (int i = 1; i <= n; i++){ 
        memset(vis, false, sizeof(vis)); 
        if (dfs(i))
           ans++;
        //else printf("%d\n", i);
    } 
    printf("%d\n", ans);
    return 0;
}