HDU 2686 Matrix 费用流
2014-10-28 16:09
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//author: CHC //First Edit Time: 2014-09-21 22:25 //Last Edit Time: 2014-09-21 23:19 #include <iostream> #include <cstdio> #include <cstring> #include <cmath> #include <set> #include <vector> #include <map> #include <queue> #include <set> #include <algorithm> #include <limits.h> using namespace std; typedef long long LL; const int MAXN=1e+4; const int MAXM=1e+5; const int INF = INT_MAX; struct Edge { int from,to,ci,cost,next; Edge(){} Edge(int _from,int _to,int _ci,int _cost,int _next):from(_from),to(_to),ci(_ci),cost(_cost),next(_next){} }e[MAXM]; int head[MAXN],tot; int q[MAXM]; int dis[MAXN],pre[MAXN],rec[MAXN],vis[MAXN]; inline void init(){ memset(head,-1,sizeof(head)); tot=0; } inline void AddEdge1(int u,int v,int ci,int cost){ e[tot]=Edge(u,v,ci,cost,head[u]); head[u]=tot++; e[tot]=Edge(v,u,0,-cost,head[v]); head[v]=tot++; } inline bool spfa(int S,int T,LL &cost,LL &flow){ int i,h=0,t=0; for(i=0;i<=MAXN;i++){ dis[i]=INF; vis[i]=false; } q[h]=S; dis[S]=0; vis[S]=true; while(h<=t){ int u=q[h++]; vis[u]=false; for(i=head[u];~i;i=e[i].next){ int v=e[i].to; if(e[i].ci>0&&dis[v]>dis[u]+e[i].cost){ dis[v]=dis[u]+e[i].cost; pre[v]=u; rec[v]=i; if(!vis[v]){ vis[v]=1; q[++t]=v; } } } } if(dis[T]==INF)return false; int minn=INF; for(i=T;i!=S;i=pre[i]){ if(e[rec[i]].ci<minn) minn=e[rec[i]].ci; } for(i=T;i!=S;i=pre[i]){ //cost+=minn*e[rec[i]].cost; e[rec[i]].ci-=minn; e[rec[i]^1].ci+=minn; } cost+=dis[T]*minn; flow+=minn; return true; } inline void mincostmaxflow(int S,int T,LL &cost,LL &flow){ while(spfa(S,T,cost,flow)); } int map1[31][31]; int main() { int n,m; while(~scanf("%d",&n)){ m=n; init(); for(int i=1;i<=n;i++){ for(int j=1;j<=n;j++){ scanf("%d",&map1[i][j]); } } int s=0,t=1; for(int i=1;i<=n;i++){ for(int j=1;j<=n;j++){ if(i==1&&j==1){ AddEdge1(s,i*n+j,2,0); AddEdge1(i*n+j,(i+n)*n+j,2,0); } else if(i==n&&j==n){ AddEdge1((i+n)*n+j,t,2,0); AddEdge1(i*n+j,(i+n)*n+j,2,0); } else AddEdge1(i*n+j,(i+n)*n+j,1,0); if(i+1<=n){ AddEdge1((i+n)*n+j,(i+1)*n+j,1,-map1[i+1][j]); } if(j+1<=n){ AddEdge1((i+n)*n+j,(i)*n+j+1,1,-map1[i][j+1]); } } } LL cost=0,flow=0; mincostmaxflow(s,t,cost,flow); cost=-cost; cost-=map1 ; cost+=map1[1][1]; printf("%I64d\n",cost); } return 0; }
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