/**//*
dinic算法，边表存储（仿指针），实用于稀疏图，O(mn^2)
*/
#include<iostream>
using namespace std;
const int maxn=205; //最大定点数
const int maxm=205; //最大边数
const int inf=0x7fffffff;
struct Edge
{
int ver; //下一顶点
int flow; //
int next; //下一条边
int op; //反向边
}edge[2*maxm];
int head[maxn]; //i顶点引出的首条边序号为head[i];
int level[maxn]; //
int m,n,src,sin; //边数，顶点数，源点，汇点
int tot; //边序号
int min(int a,int b)
{
return a<b? a:b;
}
void add_edge(int u,int v,int w)
{
edge[tot].ver=v;
edge[tot].flow=w;
edge[tot].next=head[u];
head[u]=tot++;
edge[tot].ver=u;
edge[tot].flow=0;
edge[tot].next=head[v];
head[v]=tot++;
edge[head[u]].op=head[v];
edge[head[v]].op=head[u];
}
void bfs_level()
{
memset(level,-1,sizeof(level));
int q[maxn],front=0,rear=0;
level[src]=0;
q[rear++]=src;
while(front<rear)
{
int k=q[front++];
for(int i=head[k];i!=-1;i=edge[i].next)
{
if(level[edge[i].ver]==-1&&edge[i].flow>0)
{
level[edge[i].ver]=level[k]+1;
q[rear++]=edge[i].ver;
}
}
}
}
int dfs_maxflow()
{
int flow=0;
int stk[maxn],top=0,mint; //栈，栈顶指针，可改进流量
bool vis[maxn];
int prt[maxn]; //记录可增广路径
int curedge[maxn]; //记录每个顶点引出的当前边序号
int i,j,curptr;
memset(vis,false,sizeof(vis));
for(i=1;i<=n;i++) curedge[i]=head[i];
stk[top]=src;
while(top>=0)
{
if(stk[top]==sin)
{
mint=inf;
for(j=top;j>=1;j--)
mint=min(mint,edge[prt[stk[j]]].flow);
for(j=top;j>=1;j--)
{
edge[prt[stk[j]]].flow-=mint;
edge[edge[prt[stk[j]]].op].flow+=mint;
if(edge[prt[stk[j]]].flow==0) curptr=j;
}
top=curptr-1;
flow+=mint;
}
else
{
for(i=curedge[stk[top]];i!=-1;i=edge[i].next)
{
if(!vis[edge[i].ver]&&level[edge[i].ver]==level[stk[top]]+1&&edge[i].flow>0)
{
curedge[stk[top]]=edge[i].next;
stk[++top]=edge[i].ver;
prt[stk[top]]=i;
break;
}
}
if(i==-1)
{
vis[stk[top]]=true;
top--;
}
}
}
return flow;
}
int dinic()
{
int maxflow=0, t;
while(1)
{
bfs_level();
if(level[sin]==-1) return maxflow;
t=dfs_maxflow();
if(!t) break;
maxflow+=t;
}
return maxflow;
}
int main()
{
while(scanf("%d%d",&m,&n)!=EOF)
{
int u,v,w;
src=1;
sin=n;
tot=0;
memset(head,-1,sizeof(head));
for(int i=0;i<m;i++)
{
scanf("%d%d%d",&u,&v,&w);
add_edge(u,v,w);
}
printf("%d\n",dinic());
}
return 0;
}
posted on 2011-05-10 13:07
wuxu 阅读(280)
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