文章標題 HDU 3549 ： Flow Problem （最大流--模板）

題目 鏈接

求點1到N 的最大流

代碼：

#include<iostream>
#include<string>
#include<cstdio>
#include<cstring>
#include<vector>
#include<math.h>
#include<map>
#include<queue> 
#include<algorithm>
using namespace std;
const int inf = 0x3f3f3f3f;
typedef pair<int,int> pii;

const int maxn=1006<<1;

int n,m;

struct node {
    int v,nex,cap,flow;
};

struct Dinic{
    int head[maxn];
    int st,la;//源點和匯點 
    int vis[maxn],tot;
    node edge[maxn];

    void init(){
        tot=0;
        memset (head,-1,sizeof (head));
    }

    void addedge(int u,int v,int c){
        edge[tot]=node{v,head[u],c,0};
        head[u]=tot++;
        edge[tot]=node{u,head[v],0,0};
        head[v]=tot++;
    } 

    int bfs(){
        memset (vis,0,sizeof (vis));
        queue<int>q;
        q.push(st);
        vis[st]=1;
        while (!q.empty()){
            int u=q.front();q.pop();
            for (int i=head[u];i!=-1;i=edge[i].nex){
                int v=edge[i].v,cap=edge[i].cap,flow=edge[i].flow;
                if(vis[v]==0&&cap>flow){
                    vis[v]=vis[u]+1;
                    if (v==la){
                        return 1;
                    }
                    q.push(v);
                } 
            } 
        }
        return 0;
    }

    int dfs(int u,int flow){
        if (u==la||flow==0){
            return flow;
        }
        int ans=0,tmp;
        for (int i=head[u];i!=-1;i=edge[i].nex){
            int v=edge[i].v,cap=edge[i].cap,f=edge[i].flow;
            if ((vis[v]==vis[u]+1)&&(tmp=dfs(v,min(cap-f,flow)))>0){
                edge[i].flow+=tmp;
                edge[i^1].flow-=tmp;
                ans+=tmp;
                flow-=tmp;
                if (flow==0)break;
            }
        }
        return ans;
    }

    int max_flow(int s,int t){
        this->st=s;
        this->la=t;
        int ans=0;
        while (bfs()){
            while (1){
                int tmp=dfs(st,inf);
                if (tmp==0)break;
                ans+=tmp;
            }
        }
        return ans;
    }
}dinic;


int main ()
{
    int T;
    scanf ("%d",&T);
    int cnt=1;
    while(T--){
        dinic.init();
        scanf ("%d%d",&n,&m);
        int u,v,c;
        for (int i=0;i<m;i++){
            scanf ("%d%d%d",&u,&v,&c);
            dinic.addedge(u,v,c);
        }
        printf ("Case %d: %d\n",cnt++,dinic.max_flow(1,n));
    } 
    return 0;
}