网络流24题1

菜鸡开始学习网络流

https://loj.ac/problem/6001

#include <iostream>
#include <cstring>
#include <queue>
#include <stdio.h>
using namespace std;
const int maxn = 2000;

int tot=0;
int head[maxn];
struct edge{
    int v,nex,w;
}e[maxn*2];
void addedge(int u,int v,int w){
    e[tot] = (edge){v,head[u],w};
    head[u] = tot++;
    e[tot] = (edge){u,head[v],0};
    head[v] = tot++;
}
int deep[maxn];
bool bfs(int S,int T){
    queue<int> q;
    memset(deep,0,sizeof(deep));
    deep[S] = 1;
    q.push(S);
    while(!q.empty()){
        int now = q.front();
        q.pop();
        for(int i=head[now];i!=-1;i=e[i].nex){
            int v = e[i].v;
            int w = e[i].w;
            if(w<=0 || deep[v]!=0) continue;
            deep[v] = deep[now]+1;
            q.push(v);
        }
    }
    return deep[T];
}
int dfs(int now,int T,int maxflow){
    if(now==T) return maxflow;
    int all = 0;
    for(int i=head[now];i!=-1 && all<maxflow;i=e[i].nex){
        int v = e[i].v;
        int w = e[i].w;
        if(deep[v]!=deep[now]+1 || w<=0) continue;
        int tt = dfs(v,T,min(maxflow-all,w));
        e[i].w-=tt;
        e[i^1].w+=tt;
        all+=tt;
    }
    return all;
}
int dinic(int S,int T){
    int ret = 0;
    while(bfs(S,T)){
        ret+=dfs(S,T,0x3f3f3f3f);
    }
    return ret;
}
int main()
{
    int n,m;
    scanf("%d%d",&n,&m);
    memset(head,-1,sizeof(head));
    int u,v;
    while(~scanf("%d%d",&u,&v)){
        addedge(u,v,1);
    }
    for(int i=1;i<=m;i++){
        addedge(0,i,1);
    }
    for(int i=m+1;i<=n;i++){
        addedge(i,n+1,1);
    }
    int ans = dinic(0,n+1);
    printf("%d\n",ans);
    return 0;
}