最大流模版

#include<iostream>
#include<algorithm>
#include<vector>
#include<cstring>
using namespace std;
struct node{
    int to,rev,f;
};
int read(){  
    int x=0; char ch=getchar();  
    while (ch<‘0‘ || ch>‘9‘) ch=getchar();  
    while (ch>=‘0‘ && ch<=‘9‘){ x=x*10+ch-‘0‘; ch=getchar(); }  
    return x;  
}  
const int maxn=10010,inf=99999999;
vector<node>map[maxn];
void add_edge(int s,int t,int f){
    map[s].push_back((node){t,map[t].size(),f});
    map[t].push_back((node){s,map[s].size()-1,0});
}
bool book[maxn];
int dfs(int s,int t,int d){
    book[s]=1;
    if(s==t){
        return d;
    }
    for(int i=0;i<map[s].size();++i){
        if(book[map[s][i].to]||map[s][i].f<=0)continue;
        int k=dfs(map[s][i].to,t,min(d,map[s][i].f));
        if(k<=0)continue;
        map[s][i].f-=k;
        map[map[s][i].to][map[s][i].rev].f+=k;
        return k;
    }
    return 0;
}
int max_flow(int s,int t){
    int ret=0;
    while(1){
        memset(book,0,sizeof(book));
        int k=dfs(s,t,inf);
        if(!k)break;
        ret+=k;
    }
    return ret;
}
int main(){
    int n,m,s,t;
    cin>>n>>m>>s>>t;
    for(int i=1;i<=m;++i){
        int s=read(),t=read(),f=read();
        add_edge(s,t,f);
    }
    cout<<max_flow(s,t);
    return 0;
}

#include<cstdio>
#include<algorithm>
#include<vector>
#include<cstring>
#include<queue>
using namespace std;
const int maxn=10010,inf=99999999;
struct node{
    int to,w,rev;
};
int iter[maxn],level[maxn],n;
vector<node>map[maxn];
void add_edge(int s,int t,int w){
    map[s].push_back((node){t,w,map[t].size()});
    map[t].push_back((node){s,0,map[s].size()-1});
}
int dfs(int s,int t,int k){
    if(s==t){
        return k;
    }
    for(int &i=iter[s];i<map[s].size();++i){
        if(level[map[s][i].to]>level[s]&&map[s][i].w>0){
            int d=dfs(map[s][i].to,t,min(k,map[s][i].w));
            if(d>0){
                map[s][i].w-=d;
                map[map[s][i].to][map[s][i].rev].w+=d;
                return d;
            }
        }
    }
    return -1;
}
void bfs(int s){
    memset(level,-1,sizeof(level));
    queue<int>q;
    level[s]=0;
    q.push(s);
    while(!q.empty()){
        int v=q.front();
        q.pop();
        for(int i=0;i<map[v].size();++i){
            if(level[map[v][i].to]<0&&map[v][i].w>0){
                level[map[v][i].to]=level[v]+1;
                q.push(map[v][i].to);
            }
        }
    }
}
int max_flow(int s,int t){
    int ret=0;
    for(;;){
        bfs(s);
        if(level[t]<0)break;
        memset(iter,0,sizeof(iter));
        while(1){
            int d=dfs(s,t,inf);
            if(d==-1)break;
            ret+=d;
        }
    }
    return ret;
}
int main(){
    int m,s,t;
    scanf("%d%d%d%d",&n,&m,&s,&t);
    for(int i=1;i<=m;++i){
        int s,t,w;
        scanf("%d%d%d",&s,&t,&w);
        add_edge(s,t,w);
    }
    printf("%d",max_flow(s,t));
    return 0;
}