noip 关押罪犯

正解：咕咕

#include<bits/stdc++.h>
using namespace std;
const int N=3e4,M=3e5; 
int vis[N],f[N],n,m,tot,mid,miner=1000000009,maxer=0;
struct re{
    int d;
    int v;
    int nex;
};
re edge[M];
void ad(int x,int y,int w){
    tot++;
    edge[tot].v=y;
    edge[tot].d=w;
    edge[tot].nex=f[x];
    f[x]=tot;
} 
bool jj(int v){
    int k=f[v];
    while(k!=-1){
    int x=edge[k].v;
    int w=edge[k].d;
    if(w>mid){
    if(vis[v]==vis[x])return 0;
    if(!vis[x]){
    vis[x]=3-vis[v];
    if(!jj(x))return 0; 
        }
    } 
    k=edge[k].nex;
    }
    return 1;
} 
bool ok(){
    bool az;
    vis[1]=1;
    az=jj(1);
    if(!az)return 0;
    for(int i=2;i<=n;i++)
    if(!vis[i]){
    vis[i]=1;
    az=jj(i);
    if(!az)return 0;
    }
    return 1;
}
int main(){
    //freopen("p.in","r",stdin);
    memset(f,-1,sizeof(f));
    cin>>n>>m;
    for(int i=1;i<=m;i++){
    int a,b,c;
    cin>>a>>b>>c;
    ad(a,b,c);
    ad(b,a,c);
    miner=min(miner,c);
    maxer=max(maxer,c);
    }
    int l=miner,r=maxer;
    mid=0;if(ok()){cout<<0;return 0;}
    while(l+1<r){
    memset(vis,0,sizeof(vis));
    mid=(l+r)>>1;
    int az=ok();
    if(az)r=mid;
      else l=mid;
    } 
    int az=ok();
    cout<<r;
    return 0;
}