【LOJ101】最大流（Dinic）

problem

• 给定n个点，m条边的有向图
• 求源点s到汇点的最大流

solution

最大流模板，，不会看笔记吧。。。

codes

#include<iostream>
#include<algorithm>
#include<queue>
#include<cstring>
using namespace std;
typedef long long LL;
const int maxn = 110, maxm = 5050<<1;
//Grape
int tot=1, head[maxn], Next[maxm], ver[maxm], edge[maxm];
void AddEdge(int x, int y, int z){
    ver[++tot] = y;  edge[tot] = z;
    Next[tot] = head[x]; head[x] = tot;
    ver[++tot] = x;  edge[tot] = 0;
    Next[tot] = head[y];  head[y] = tot;
}
//maxflow
int s, t;
queue<int>q;
LL dep[maxn];//到x最少需要经过的边数
bool bfs(){
    memset(dep,0,sizeof(dep));
    while(q.size())q.pop();
    q.push(s); dep[s] = 1;
    while(q.size()){
        int x = q.front();  q.pop();
        for(int i = head[x]; i; i = Next[i]){
            if(edge[i] && !dep[ver[i]]){
                q.push(ver[i]);
                dep[ver[i]] = dep[x]+1;
                if(ver[i] == t)return true;
            }
        }
    }
    return false;
}
int dinic(int x, int flow){
    if(x == t)return flow;
    int rest = flow;
    for(int i = head[x]; i && rest; i = Next[i]){
        if(edge[i] && dep[ver[i]]==dep[x]+1){
            int k = dinic(ver[i], min(rest, edge[i]));
            if(!k)dep[ver[i]] = 0;
            edge[i] -= k;
            edge[i^1] += k;
            rest -= k;
        }
    }
    return flow-rest;
}
LL Maxflow(){
    LL maxflow = 0, flow;
    while(bfs())
        while(flow=dinic(s,1<<30))maxflow += flow;
    return maxflow;
}

int n, m;
void input(){
    cin>>n>>m>>s>>t;
    for(int i = 1; i <= m; i++){
        int x, y, z;  cin>>x>>y>>z;  AddEdge(x,y,z);
    }
}

int main(){
    ios::sync_with_stdio(false);
    input();
    cout<<Maxflow()<<'
';
    return 0;
}