HDU 2255 奔小康赚大钱

hdu 2255

费用流的模板题。

就是用KM跑一下最优匹配就好了。

代码：

#include<bits/stdc++.h>
using namespace std;
#define Fopen freopen("_in.txt","r",stdin); freopen("_out.txt","w",stdout);
#define LL long long
#define ULL unsigned LL
#define fi first
#define se second
#define pb push_back
#define lson l,m,rt<<1
#define rson m+1,r,rt<<1|1
#define max3(a,b,c) max(a,max(b,c))
#define min3(a,b,c) min(a,min(b,c))
typedef pair<int,int> pll;
const int inf = 0x3f3f3f3f;
const LL INF = 0x3f3f3f3f3f3f3f3f;
const LL mod =  (int)1e9+7;
const int N = 310;
int val[N][N];
int lx[N], ly[N], match[N];
int visx[N], visy[N];
int slack[N];
int n;
void init(){
    memset(match, -1, sizeof(match));
    memset(ly, 0, sizeof(ly));
    memset(lx, -inf, sizeof(lx));
}
bool hunger(int u){
    visx[u] = 1;
    for(int i = 1; i <= n; i++){
        if(visy[i]) continue;
        else {
            if(lx[u] + ly[i] == val[u][i]){
                visy[i] = 1;
                if(match[i] == -1 || hunger(match[i])){
                    match[i] = u;
                    return true;
                }
            }
            else slack[i] = min(slack[i], lx[u]+ly[i] - val[u][i]);
        }
    }
    return false;

}
void KM_perferct_match(){
    for(int i = 1; i <= n; i++)
        for(int j = 1; j <= n; j++)
            lx[i] = max(lx[i], val[i][j]);
    for(int i = 1; i <= n; i++){
        memset(slack, inf, sizeof(slack));
        while(1){
            memset(visx, 0, sizeof(visx));
            memset(visy, 0, sizeof(visy));
            if(hunger(i)) break;
            else {
                int tmp = inf;
                for(int j = 1; j <= n; j++)
                    if(!visy[j]) tmp = min(tmp, slack[j]);
                ///if(tmp == inf) break;
                for(int j = 1; j <= n; j++){
                    if(visx[j]) lx[j] -= tmp;
                    if(visy[j]) ly[j] += tmp;
                    else slack[j] -= tmp;
                }
            }
        }
    }
}
int main(){

    while(~scanf("%d", &n)){
        init();
        for(int i = 1; i <= n; i++)
            for(int j = 1; j <= n; j++)
                scanf("%d", &val[i][j]);
        KM_perferct_match();
        int ans = 0;
        for(int i = 1; i <= n; i++){
            if(match[i] != -1) ans += val[match[i]][i];
        }
        printf("%d
", ans);
    }
    return 0;
}

 注意的就是在这个跑法中，得到的结果是最大匹配的最大值是多少。

如果要求最小值的话，将值取反，变成负数，然后再套模板，跑出结果，最后再取反就是最小值了。