POJ2455Secret Milking Machine[最大流 无向图 二分答案]

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
using namespace std;
const int N=205,INF=1e9;
int read(){
    char c=getchar();int x=0,f=1;
    while(c<‘0‘||c>‘9‘){if(c==‘-‘)f=-1; c=getchar();}
    while(c>=‘0‘&&c<=‘9‘){x=x*10+c-‘0‘; c=getchar();}
    return x*f;
}
int n,m,T,u,v,w,s,t;
struct edge{
    int v,ne,w,c,f;
}e[N*N<<1];
struct data{
    int u,v,w;
}a[N*N];
int h[N],cnt=0;
inline void ins(int u,int v,int w,int c){//printf("ins %d %d %d\n",u,v,w);
    cnt++;
    e[cnt].v=v;e[cnt].c=c;e[cnt].f=0;e[cnt].w=w;e[cnt].ne=h[u];h[u]=cnt;
    cnt++;
    e[cnt].v=u;e[cnt].c=c;e[cnt].f=0;e[cnt].w=w;e[cnt].ne=h[v];h[v]=cnt;
}

int cur[N];
int q[N],head,tail,vis[N],d[N];

void build(int mid){
    cnt=0;
    memset(h,0,sizeof(h));
    for(int i=1;i<=m;i++) if(a[i].w<=mid) ins(a[i].u,a[i].v,a[i].w,1);
}
bool bfs(int mid){
    memset(vis,0,sizeof(vis));
    memset(d,0,sizeof(d));
    head=tail=1;
    q[tail++]=s;d[s]=0;vis[s]=1;
    while(head!=tail){
        int u=q[head++];
        for(int i=h[u];i;i=e[i].ne){
            int v=e[i].v;
            if(!vis[v]&&e[i].f<e[i].c){
                q[tail++]=v;vis[v]=1;
                d[v]=d[u]+1;
                if(v==t) return 1;
            }
        }    
    }
    return 0;
}
int dfs(int u,int a){//printf("dfs %d %d\n",u,a);
    if(u==t||a==0) return a;
    int flow=0,f;
    for(int &i=cur[u];i;i=e[i].ne){
        int v=e[i].v;
        if(d[v]==d[u]+1&&(f=dfs(v,min(a,e[i].c-e[i].f)))>0){
            flow+=f;
            e[i].f+=f;
            e[((i-1)^1)+1].f-=f;
            a-=f;
            if(a==0) break;
        }
    }
    return flow;
}
int dinic(int mid){
    int flow=0;
    while(bfs(mid)){
        for(int i=s;i<=t;i++) cur[i]=h[i];
        flow+=dfs(s,INF);
    }
    //printf("flow %d\n",flow);
    return flow;
}

int main(){
    n=read();m=read();T=read();s=1;t=n;
    int l=INF,r=0,ans=INF;
    for(int i=1;i<=m;i++){
        u=read();v=read();w=read(); r=max(r,w);l=min(l,w);
        //ins(u,v,w,1);
        a[i].u=u;a[i].v=v;a[i].w=w;
    }
    while(l<=r){
        int mid=(l+r)>>1;//printf("hi %d %d %d\n",l,r,mid);
        build(mid);
        if(dinic(mid)>=T) ans=min(ans,mid),r=mid-1;
        else l=mid+1;
    }
    printf("%d",ans);
}