http://poj.org/problem?id=3422
最小费用最大流 求的时候把边加为负的 输出的时候再负回来 就变成求的最大费用了
拆点 一个点拆为 i i' i->i'连两条边 一条cap为0 cost为给出的值 另一条cap为INF cost为0 ，i'到右和下分别设置一条边cap为INF cost为0 设置超级源点到1节点 cap为K cost为0
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1 #include <iostream> 2 #include<cstdio> 3 #include<cstring> 4 #include<algorithm> 5 #include<stdlib.h> 6 #include<queue> 7 #define INF 0xfffffff 8 #define MN 50500 9 #define MM 100100 10 using namespace std; 11 struct node 12 { 13 int u,v,cost,cap,next; 14 }edge[MM]; 15 int head[MN],t,vis[MN],dist[MN],pp[MN]; 16 void init() 17 { 18 t =0; 19 memset(head,-1,sizeof(head)); 20 } 21 void add(int u,int v,int c,int p) 22 { 23 edge[t].u = u; 24 edge[t].v = v; 25 edge[t].cap = c; 26 edge[t].cost = p; 27 edge[t].next = head[u]; 28 head[u] = t++; 29 edge[t].u = v; 30 edge[t].v = u; 31 edge[t].cap = 0; 32 edge[t].cost = -p; 33 edge[t].next = head[v]; 34 head[v] = t++; 35 } 36 int spfa(int s,int en,int n) 37 { 38 int u,v,i; 39 memset(vis,0,sizeof(vis)); 40 memset(pp,-1,sizeof(pp)); 41 for(i = 0 ; i <= n ; i++) 42 dist[i] =INF; 43 queue<int>q; 44 dist[s] = 0; 45 vis[s] = 1; 46 q.push(s); 47 while(!q.empty()) 48 { 49 u = q.front(); 50 q.pop(); 51 vis[u] = 0; 52 //cout<<u<<endl; 53 for(i = head[u] ; i != -1 ; i = edge[i].next) 54 { 55 v = edge[i].v; 56 if(edge[i].cap&&dist[v]>dist[u]+edge[i].cost) 57 { 58 dist[v] = dist[u]+edge[i].cost; 59 pp[v] = i; 60 if(!vis[v]) 61 { 62 vis[v] = 1; 63 q.push(v); 64 } 65 } 66 } 67 } 68 //cout<<dist[en]<<endl; 69 if(dist[en]==INF) 70 return 0; 71 return 1; 72 } 73 int mcmf(int s,int en,int n) 74 { 75 int i,mc=0,minf; 76 while(spfa(s,en,n)) 77 { 78 minf = INF+1; 79 for(i = pp[en] ; i!= -1 ; i = pp[edge[i].u]) 80 { 81 if(minf>edge[i].cap) 82 minf = edge[i].cap; 83 } 84 for(i = pp[en] ; i != -1; i = pp[edge[i].u]) 85 { 86 edge[i].cap -= minf; 87 edge[i^1].cap+=minf; 88 } 89 //cout<<minf<<" "<<dist[en]<<endl; 90 mc+=minf*dist[en]; 91 } 92 return mc; 93 } 94 int main() 95 { 96 int i,j,k,n,m,a; 97 while(cin>>n>>k) 98 { 99 init(); 100 int s = 0,en = 2*n*n+1; 101 add(s,1,k,0); 102 add(2*n*n,en,k,0); 103 for(i = 1; i <= n ; i++) 104 for(j = 1; j <= n ; j++) 105 { 106 cin>>a; 107 add((i-1)*n+j,(i-1)*n+j+n*n,1,-a); 108 add((i-1)*n+j,(i-1)*n+j+n*n,INF,0); 109 if(i<n) 110 add((i-1)*n+j+n*n,i*n+j,INF,0); 111 if(j<n) 112 add((i-1)*n+j+n*n,(i-1)*n+j+1,INF,0); 113 } 114 cout<<-mcmf(s,en,en)<<endl; 115 } 116 return 0; 117 }