【bzoj1507】 JSOI2008—Blue Mary的旅行

// bzoj1570
#include<algorithm>
#include<iostream>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<cmath>
#include<queue>
#define LL long long
#define inf (1ll<<30)
#define free(a) freopen(a".in","r",stdin),freopen(a".out","w",stdout)
using namespace std;

const int maxn=1000010;
int head[maxn],n,m,T,et,ans,cnt=1;
struct data {int u,v,w;}t[maxn];
struct edge {int to,next,w;}e[maxn];

void link(int u,int v,int w) {
	e[++cnt]=(edge){v,head[u],w};head[u]=cnt;
	e[++cnt]=(edge){u,head[v],0};head[v]=cnt;
}

namespace Dinic {
	int d[maxn],s,t;
	bool bfs(int s,int t) {
		memset(d,-1,sizeof(d));
		queue<int> q;q.push(s);d[s]=0;
		while (!q.empty()) {
			int x=q.front();q.pop();
			for (int i=head[x];i;i=e[i].next)
				if (e[i].w && d[e[i].to]<0) d[e[i].to]=d[x]+1,q.push(e[i].to);
		}
		return d[t]>0;
	}
	int dfs(int x,int f) {
		if (x==t || f==0) return f;
		int w,used=0;
		for (int i=head[x];i;i=e[i].next) if (e[i].w && d[e[i].to]==d[x]+1) {
				w=dfs(e[i].to,min(e[i].w,f-used));
				used+=w;e[i].w-=w;e[i^1].w+=w;
				if (used==f) return used;
			}
		if (!used) d[x]=-1;
		return used;
	}
	int main(int x,int y) {
		s=x,t=y;int flow=0;
		while (bfs(x,y)) flow+=dfs(x,inf);
		return flow;
	}
}

int main() {
	scanf("%d%d%d",&n,&m,&T);
	for (int i=1;i<=m;i++) scanf("%d%d%d",&t[i].u,&t[i].v,&t[i].w);
	link(0,1,T);et=1000000;
	for (int i=0;1;i++) {
		for (int j=1;j<=n;j++) link(i*n+j,(i+1)*n+j,inf);
		for (int j=1;j<=m;j++) link(i*n+t[j].u,(i+1)*n+t[j].v,t[j].w);
		link((i+1)*n,et,inf);
		ans+=Dinic::main(0,et);
		if (ans==T) {printf("%d",i);break;}
	}
	return 0;
}