uva 11380(最大流+拆点）

题目链接：http://acm.hust.edu.cn/vjudge/problem/viewProblem.action?id=36707

思路：根据题意拆点建图即可。

  1 #include<iostream>

  2 #include<cstdio>

  3 #include<cstring>

  4 #include<algorithm>

  5 #include<queue>

  6 using namespace std;

  7 #define MAXN 2222

  8 #define inf 1<<30

  9 

 10 struct Edge{

 11     int v,cap,next;

 12 }edge[MAXN*MAXN];

 13 

 14 int n,m,p,NE,NV,vs,vt;

 15 int head[MAXN];

 16 

 17 void Insert(int u,int v,int cap)

 18 {

 19     edge[NE].v=v;

 20     edge[NE].cap=cap;

 21     edge[NE].next=head[u];

 22     head[u]=NE++;

 23 

 24     edge[NE].v=u;

 25     edge[NE].cap=0;

 26     edge[NE].next=head[v];

 27     head[v]=NE++;

 28 }

 29 

 30 int level[MAXN],gap[MAXN];

 31 void bfs(int vt)

 32 {

 33     memset(level,-1,sizeof(level));

 34     memset(gap,0,sizeof(gap));

 35     level[vt]=0;

 36     gap[0]++;

 37     queue<int>que;

 38     que.push(vt);

 39     while(!que.empty()){

 40         int u=que.front();

 41         que.pop();

 42         for(int i=head[u];i!=-1;i=edge[i].next){

 43             int v=edge[i].v;

 44             if(level[v]!=-1)continue;

 45             level[v]=level[u]+1;

 46             gap[level[v]]++;

 47             que.push(v);

 48         }

 49     }

 50 }

 51 

 52 int cur[MAXN],pre[MAXN];

 53 int SAP(int vs,int vt)

 54 {

 55     bfs(vt);

 56     memset(pre,-1,sizeof(pre));

 57     memcpy(cur,head,sizeof(head));

 58     int u=pre[vs]=vs,aug=inf,maxflow=0;

 59     gap[0]=NV;

 60     while(level[vs]<NV){

 61         bool flag=false;

 62         for(int &i=cur[u];i!=-1;i=edge[i].next){

 63             int v=edge[i].v;

 64             if(edge[i].cap>0&&level[u]==level[v]+1){

 65                 flag=true;

 66                 aug=min(aug,edge[i].cap);

 67                 pre[v]=u;

 68                 u=v;

 69                 if(v==vt){

 70                     maxflow+=aug;

 71                     for(u=pre[u];v!=vs;v=u,u=pre[u]){

 72                         edge[cur[u]].cap-=aug;

 73                         edge[cur[u]^1].cap+=aug;

 74                     }

 75                     aug=inf;

 76                 }

 77                 break;

 78             }

 79         }

 80         if(flag)continue;

 81         int minlevel=NV;

 82         for(int i=head[u];i!=-1;i=edge[i].next){

 83             int v=edge[i].v;

 84             if(edge[i].cap>0&&level[v]<minlevel){

 85                 minlevel=level[v];

 86                 cur[u]=i;

 87             }

 88         }

 89         if(--gap[level[u]]==0)break;

 90         level[u]=minlevel+1;

 91         gap[level[u]]++;

 92         u=pre[u];

 93     }

 94     return maxflow;

 95 }

 96 

 97 char map[44][44];

 98 int dir[4][2]={{-1,0},{1,0},{0,-1},{0,1}};

 99 

100 int main()

101 {

102     while(~scanf("%d%d%d",&n,&m,&p)){

103         for(int i=0;i<n;i++)scanf("%s",map[i]);

104         NE=0;

105         vs=0,vt=2*n*m+1,NV=2*n*m+2;

106         memset(head,-1,sizeof(head));

107         for(int i=0;i<n;i++){

108             for(int j=0;j<m;j++){

109                 if(map[i][j]=='~')continue;

110                 for(int k=0;k<4;k++){

111                     int x=i+dir[k][0],y=j+dir[k][1];

112                     if(x<0||x>=n||y<0||y>=m)continue;

113                     Insert(i*m+j+1+n*m,x*m+y+1,inf);

114                 }

115                 if(map[i][j]=='*'){

116                     Insert(vs,i*m+j+1,1);

117                     Insert(i*m+j+1,i*m+j+1+n*m,1);

118                 }

119                 else if(map[i][j]=='.')Insert(i*m+j+1,i*m+j+1+n*m,1);

120                 else if(map[i][j]=='@')Insert(i*m+j+1,i*m+j+1+n*m,inf);

121                 else if(map[i][j]=='#')Insert(i*m+j+1,i*m+j+1+n*m,inf),Insert(i*m+j+1+n*m,vt,p);

122             }

123         }

124         printf("%d\n",SAP(vs,vt));

125     }

126     return 0;

127 }

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