HDU 3376 Matrix Again 费用流

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//author: CHC//First Edit Time:2014-09-21 22:25//Last Edit Time:2014-09-21 23:24#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+6;const int MAXM=1e+7;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[610][610];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[n][n];        cost+=map1[1][1];        printf("%I64d\n",cost);    }    return 0;}
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