最大流模版 EK

EK算法基于增广路的思想,易于理解,但由于低效并不被经常使用

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <cmath>
#include <queue>
using namespace std;
const int MAXN=10005,MAXM=100005;
int n,m,s,flow,t,nume,head[MAXN],delta[MAXN],pre[MAXN];
queue<int> q;
struct edge{
	int to,nxt,cap,flow;
}e[MAXM<<1];
void adde(int from,int to,int cap){
	e[++nume].to=to;
	e[nume].cap=cap;
	e[nume].flow=0;
	e[nume].nxt=head[from];
	head[from]=nume;
}
int init(){
	int rv=0,fh=1;
	char c=getchar();
	while(c<'0'||c>'9'){
		if(c=='-') fh=-1;
		c=getchar();
	}
	while(c>='0'&&c<='9'){
		rv=(rv<<1)+(rv<<3)+c-'0';
		c=getchar();
	}
	return fh*rv;
}
int main(){
	n=init();m=init();s=init();t=init();
	for(int i=1;i<=m;i++){
		int u=init(),v=init(),cap=init();
		adde(u,v,cap);
		adde(v,u,0);
	}
	while(1){
		memset(delta,0,sizeof(delta));
		while(!q.empty()) q.pop();
		q.push(s);delta[s]=0x3f3f3f3f;pre[s]=0;
		while(!q.empty()){
			int u=q.front();q.pop();
			for(int i=head[u];i;i=e[i].nxt){
				int v=e[i].to;
				if(!delta[v]&&e[i].flow<e[i].cap){
					delta[v]=min(delta[u],e[i].cap-e[i].flow);
					pre[v]=i;
					q.push(v);
				}
			}
			if(delta[t]) break;
		}
		if(!delta[t]) break;
		for(int i=pre[t];i;i=pre[e[((i-1)^1)+1].to]){
			e[i].flow+=delta[t];
			e[((i-1)^1)+1].flow-=delta[t];
		}
		flow+=delta[t];
	}
	printf("%d\n",flow);
}