codevs 1993 草地排水 USACO

/*Dinic*/
#include<iostream>
#include<cstdio>
#include<cstring>
#include<queue>
#define maxn 210
#define inf 0x7fffffff
using namespace std;
int n,m,num,head[maxn],cur[maxn],dis[maxn];
struct node{
    int u,v,flow,pre;
}e[maxn*2];
void Add(int from,int to,int t){
    e[num].u=from;
    e[num].v=to;
    e[num].flow=t;
    e[num].pre=head[from];
    head[from]=num++;
}
void Init(){
    scanf("%d%d",&m,&n);
    int u,v,t;
    memset(head,-1,sizeof(head));
    for(int i=1;i<=m;i++){
        scanf("%d%d%d",&u,&v,&t);
        Add(u,v,t);Add(v,u,0);
    }
}
bool Bfs(){
    memset(dis,-1,sizeof(dis));
    queue<int>q;
    q.push(1);dis[1]=0;
    while(!q.empty()){
        int k=q.front();q.pop();
        for(int i=head[k];i!=-1;i=e[i].pre){
            int v=e[i].v;
            if(dis[v]!=-1||!e[i].flow)continue;
            q.push(v);dis[v]=dis[k]+1;;
        }
    }
    return dis[n]!=-1;
}
int Dfs(int now,int lim){
    if(!lim||now==n)return lim;
    int r=0;
    for(int &i=cur[now];i!=-1;i=e[i].pre){
        int v=e[i].v,s=0;
        if(dis[v]==dis[now]+1&&(s=Dfs(v,min(lim,e[i].flow)))){
            e[i].flow-=s;r+=s;
            e[i^1].flow+=s;lim-=s;
        }
        if(lim==0)break;
    }
    return r;
}
void Dinic(){
    int ans=0;
    while(Bfs()){
        memcpy(cur,head,sizeof(head));
        ans+=Dfs(1,0x7fffffff);
    }
    printf("%d\n",ans);
}
int main()
{
    Init();
    Dinic();
    return 0;
}

 

转载于:https://www.cnblogs.com/yanlifneg/p/5865136.html