[bzoj1196][HNOI2006]公路修建问题

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
int read()
{
    int x=0,f=1;char ch=getchar();
    while(ch<‘0‘||ch>‘9‘){if(ch==‘-‘) f=-1;ch=getchar();}
    while(ch>=‘0‘&&ch<=‘9‘){x=x*10+ch-‘0‘; ch=getchar();}
    return x*f;
}

int n,m,K,s[10005];
struct edge{
    int from,to,w;
}c1[20005],c2[20005];
bool cmp(edge x,edge y){return x.w<y.w;}
int getfa(int x){return s[x]==0?x:s[x]=getfa(s[x]);}

bool check(int mid)
{
    memset(s,0,sizeof(s));int num=1,cnum=0,x,y;
    for(int i=1;i<=m&&c1[i].w<=mid;i++)
        if((x=getfa(c1[i].from))!=(y=getfa(c1[i].to)))
            s[x]=y,num++,cnum++;
    if(cnum<K)return false;
    for(int i=1;i<=m&&c2[i].w<=mid;i++)
        if((x=getfa(c2[i].from))!=(y=getfa(c2[i].to)))
            s[x]=y,num++;
    return num==n;
}

int main()
{
    n=read();K=read();m=read();
    for(int i=1;i<m;i++)
    {
        c1[i].from=c2[i].from=read();
        c1[i].to=c2[i].to=read();
        c1[i].w=read();c2[i].w=read();
    }
    sort(c1+1,c1+m+1,cmp);sort(c2+1,c2+m+1,cmp);
    int l=1,r=30000,mid,ans;
    while(l<=r)
    {
        mid=l+r>>1;
        if(check(mid)) ans=mid,r=mid-1;
        else l=mid+1;
    }
    cout<<ans;
    return 0;
}