【USACO】Dining

【题目链接】

【JZXX】点击打开链接

【caioj】点击打开链接

【算法】

拆点+网络流

【代码】

#include<bits/stdc++.h>
using namespace std;
#define MAXN 1000

int i,tot,N,F,D,sf,sd,ans,x;
int U[MAXN*5],V[MAXN*5],W[MAXN*5],Head[MAXN*5],
        Next[MAXN*5],other[MAXN*5],h[MAXN*5];

template <typename T> void read(T &x) {
        int f=1; x = 0;
        char c = getchar(); 
        for (; !isdigit(c); c = getchar()) { if (c=='-') f=-1; }
        for (; isdigit(c); c = getchar()) x=x*10+c-'0';
        x*=f;
}

inline void add(int a,int b,int c) {
        ++tot;
        U[tot] = a; V[tot] = b; W[tot] = c;
        Next[tot] = Head[a]; Head[a] = tot;
        other[tot] = tot + 1;
        ++tot;
        U[tot] = b; V[tot] = a; W[tot] = 0;
        Next[tot] = Head[b]; Head[b] = tot;
        other[tot] = tot - 1;
}

inline bool BFS() {
        int i,x,y;
        queue<int> q;    
        memset(h,0,sizeof(h)); 
        h[1] = 1; q.push(1);
        while (!q.empty()) {
                x = q.front(); q.pop();
                for (i = Head[x]; i; i = Next[i]) {
                        y = V[i];
                        if ((W[i] > 0) && (!h[y])) {
                                h[y] = h[x] + 1;
                                q.push(y);
                        }
                }
        }
        if (h[F+2*N+D+2]) return true;
        else return false;
}

int maxflow(int x,int f) {
        int i,y,s=0,t;
        if (x == F + 2 * N + D + 2) return f;
        for (i = Head[x]; i; i = Next[i]) {
                y = V[i];
                if ((W[i] > 0) && (h[y] == h[x] + 1) && (s < f)) {
                        s += (t = maxflow(y,min(W[i],f-s)));
                        W[i] -= t; W[other[i]] += t;
                }
        }    
        if (!s) h[x] = 0;
        return s;
}

int main() {
        
        read(N); read(F); read(D);
        for (i = 1; i <= F; i++) add(1,1+i,1);
        for (i = 1; i <= D; i++) add(1+F+2*N+i,F+2*N+D+2,1);
        for (i = 1; i <= N; i++) add(1+F+i,1+F+N+i,1);
        for (i = 1; i <= N; i++) {
                read(sf); read(sd);
                while (sf--) {
                        read(x);
                        add(1+x,i+F+1,1);
                }
                while (sd--) {
                        read(x);
                        add(1+F+N+i,1+F+2*N+x,1); 
                }        
        }
        
        while (BFS()) {
                ans += maxflow(1,2e9);
        }
        
        cout<< ans << endl;
        
        return 0;
    
}