Uva1349Optimal Bus Route Design(二分图最佳完美匹配)(最小值)

题意：

给定n个点的有向图问，问能不能找到若干个环，让所有点都在环中，且让权值最小，KM算法求最佳完美匹配，只不过是最小值，所以把边权变成负值，输出时将ans取负即可

这道题是在VJ上交的

 

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

const int maxn = 100 + 5;
const int inf = 0x3f3f3f3f;
bool visr[maxn], visl[maxn];
int n, delta, w[maxn][maxn], lx[maxn], ly[maxn], lft[maxn];
inline bool match( int x ){
    visl[x] = 1;
    for( int y=1; y<=n; y++ )
        if( lx[x]+ly[y]==w[x][y] && !visr[y] ){
            visr[y] = 1;
            if( !lft[y] || match(lft[y]) ){
                lft[y] = x;
                return 1;
            }
        }
    return 0;
}

inline void update(){
    for( int i=1; i<=n; i++ ) if( visl[i] )
        for( int j=1; j<=n; j++ ) if( !visr[j] )
            delta = min( delta, lx[i]+ly[j]-w[i][j] );
    for( int i=1; i<=n; i++ ){
        if( visl[i] ) lx[i] -= delta;
        if( visr[i] ) ly[i] += delta;
    }
}

inline int KM(){
    for( int i=1; i<=n; i++ ){
        lft[i] = ly[i] = 0;
        lx[i] = -inf;
        for( int j=1; j<=n; j++ )
            lx[i] = max(lx[i], w[i][j]);
    }
    for( int i=1; i<=n; i++ ){
        while(1){
            delta = inf;
            memset( visr, 0, sizeof(visr) );
            memset( visl, 0, sizeof(visl) );
            if( match(i) ) break;
            update();
        }
    }
    int res = 0;
    for( int i=1; i<=n; i++ ) res += w[lft[i]][i];
    return res;
}

int main(){
    // freopen("in.txt", "r", stdin);
    while( ~scanf("%d", &n) && n ){
        for( int i=1; i<=n; i++ ) 
            for( int j=1; j<=n; j++ ) w[i][j] = -inf;        //不能使用memset( w, -inf, sizeof(w) );
        for( int i=1; i<=n; i++ ){
            int j;
            while( ~scanf("%d", &j) && j ){
                int d;
                scanf("%d", &d);
                w[i][j] = max( -d, w[i][j] );
            }
        }
        int ans = KM();
        if( -ans>=inf ) puts("N");        
        else printf("%d\n", -ans);
    }

    return 0;
}