POJ 1274 The Perfect Stall 【二分图匹配】

裸的二分图匹配

匈牙利算法：

#include <cstdio>#include <cstring>#include <iostream>#include <vector>#include <algorithm>using namespace std;#define N 420#define INF 0x3f3f3f3fclass Dinic {public:    int c[N][N], n, s, t, l[N], e[N];    int flow(int maxf = INF) {        int left = maxf;        while (build()) left -= push(s, left);        return maxf - left;    }    int push(int x, int f) {        if (x == t) return f;        int &y = e[x], sum = f;        for (; y<n; y++)            if (c[x][y] > 0 && l[x]+1==l[y]) {                int cnt = push(y, min(sum, c[x][y]));                c[x][y] -= cnt;                c[y][x] += cnt;                sum -= cnt;                if (!sum) return f;            }        return f-sum;    }    bool build() {        int m = 0;        memset(l, -1, sizeof(l));        l[e[m++]=s] = 0;        for (int i=0; i<m; i++) for (int y=0; y<n; y++)            if (c[e[i]][y] > 0 && l[y]<0) l[e[m++]=y] = l[e[i]] + 1;        memset(e, 0, sizeof(e));        return l[t] >= 0;    }} net;int main() {    int n, m, a, b;    while (scanf("%d%d", &n, &m) == 2) {        memset(net.c, 0, sizeof(net.c));        net.s = 0, net.t = n+m+1, net.n = n+m+2;        for (int i=1; i<=n; i++) net.c[net.s][i] = 1;        for (int i=1; i<=m; i++) net.c[n+i][net.t] = 1;        for (int i=1; i<=n; i++) {            cin >> a;            while (a--) {                cin >> b;                net.c[i][n+b] = INF;            }        }        cout << net.flow() << endl;    }    return 0;}