BZOJ1733: [Usaco2005 feb]Secret Milking Machine 神秘的挤奶机

n<=200个点m<=40000条边无向图，求   t次走不经过同条边的路径从1到n的经过的边的最大值   的最小值。

最大值最小--二分，t次不重边路径--边权1的最大流。

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<algorithm>
//#include<iostream>
using namespace std;

int n,m,t;
#define maxn 211
#define maxm 160011
struct Edge{int to,next,v;}edge[maxm];int first[maxn],le=2;
void in(int x,int y,int v) {Edge &e=edge[le];e.to=y;e.v=v;e.next=first[x];first[x]=le++;}
void insert(int x,int y,int v) {in(x,y,v);in(y,x,v);}
const int inf=0x3f3f3f3f;
struct network
{
    struct Edge{int to,next,cap,flow;}edge[maxm];int first[maxn],le,n,s,t;
    void clear(int n)
    {
        memset(first,0,sizeof(first));
        le=2;this->n=n;
    }
    void in(int x,int y,int cap) {Edge &e=edge[le];e.to=y;e.cap=cap;e.flow=0;e.next=first[x];first[x]=le++;}
    void insert(int x,int y,int cap) {in(x,y,cap);in(y,x,0);}
    int que[maxn],head,tail,dis[maxn],cur[maxn];
    bool bfs()
    {
        memset(dis,0,sizeof(dis));
        dis[s]=1;
        que[head=(tail=1)-1]=s;
        while (head!=tail)
        {
            const int now=que[head++];
            for (int i=first[now];i;i=edge[i].next)
            {
                const Edge &e=edge[i];
                if (e.cap>e.flow && !dis[e.to])
                {
                    dis[e.to]=dis[now]+1;
                    que[tail++]=e.to;
                }
            }
        }
        return dis[t];
    }
    int dfs(int x,int a)
    {
        if (x==t || !a) return a;
        int flow=0,f;
        for (int &i=cur[x];i;i=edge[i].next)
        {
            Edge &e=edge[i];
            if (dis[e.to]==dis[x]+1 && (f=dfs(e.to,min(a,e.cap-e.flow)))>0)
            {
                flow+=f;
                e.flow+=f;
                edge[i^1].flow-=f;
                a-=f;
                if (!a) break;
            }
        }
        return flow;
    }
    int dinic(int s,int t)
    {
        this->s=s;this->t=t;
        int ans=0;
        while (bfs())
        {
            for (int i=1;i<=n;i++) cur[i]=first[i];
            ans+=dfs(s,inf);
        }
        return ans;
    }
}g;
bool check(int x)
{
    g.clear(n);
    for (int i=1;i<=n;i++)
        for (int j=first[i];j;j=edge[j].next)
        {
            const Edge &e=edge[j];
            if (e.v<=x) g.insert(i,e.to,1);
        }
    return g.dinic(1,n)>=t;
}
int x,y,v;
int main()
{
    scanf("%d%d%d",&n,&m,&t);
    int Max=0;
    memset(first,0,sizeof(first));
    for (int i=1;i<=m;i++)
    {
        scanf("%d%d%d",&x,&y,&v);
        insert(x,y,v);
        Max=max(Max,v);
    }
    int L=0,R=Max+1;
    while (L<R)
    {
        int mid=(L+R)>>1;
        if (check(mid)) R=mid;
        else L=mid+1;
    }
    printf("%d
",L);
    return 0;
}