Poj1273Drainage Ditches（网络流）

Posted 2020-10-20 void_f

Description

给图，求最大流

最大流模板题，这里用dinic

Code

#include <cstdio>
#include <cstring>
#include <algorithm>
#define Inf 0x7fffffff
#define N 210
using namespace std;

int g[N][N],d[N],q[N*10],h,t;
int n,m,Ans,tmp;

bool Bfs(){
    memset(d,-1,sizeof(d));
    d[1]=0;
    h=0,t=1;
    q[1]=1;
    while(h<t){
        int u=q[++h];
        for(int v=1;v<=n;++v)
            if(d[v]<0&&g[u][v]>0){
                d[v]=d[u]+1;
                q[++t]=v;
            }
    }
    return d[n]>0;
}

int dfs(int u,int low){
    if(u==n) return low;
    int tmp; 
    for(int v=1;v<=n;++v){
        if(g[u][v]>0&&d[v]==d[u]+1&&(tmp=dfs(v,min(low,g[u][v])))){
            g[u][v]-=tmp;
            g[v][u]+=tmp;
            return tmp;
        }
    }
    return 0;
}

int main(){
    while(~scanf("%d%d",&m,&n)){
        memset(g,0,sizeof(g));
        for(int i=1,u,v,f;i<=m;++i){
            scanf("%d%d%d",&u,&v,&f);
            g[u][v]+=f;
        }
        Ans=0;
        while(Bfs()) {
            while(tmp=dfs(1,Inf)) Ans+=tmp;
        }
        printf("%d\n",Ans);
    }
    return 0;
}