EZOJ #389点分治好题

分析

一层一层把叶子去掉

看最多能去掉多少层即可

代码

#include<bits/stdc++.h>
using namespace std;
int vis[],du[],fa[],n,m,ans;
int head[],to[],nxt[],cnt;
int q[],le,ri;
inline int ra(){
    int x=;char s=getchar();
    while(!isdigit(s))s=getchar();
    while(isdigit(s))x=(x<<)+(x<<)+(s-''),s=getchar();
    return x;
}
inline void add(int x,int y){
    nxt[++cnt]=head[x];
    head[x]=cnt;
    to[cnt]=y;
    nxt[++cnt]=head[y];
    head[y]=cnt;
    to[cnt]=x;
}
inline void dfs(int x,int f){
    fa[x]=f;
    for(int i=head[x];i;i=nxt[i])
      if(to[i]!=f)dfs(to[i],x);
}
int main(){
    int i,j,k;
    n=ra(),k=ra();
    k=n-k;
    for(i=;i<n;++i){
      int x,y;
      x=ra(),y=ra();
      du[x]++,du[y]++;
      add(x,y);
    }
    dfs(,);
    le=;
    for(i=;i<=n;++i)if(du[i]==)q[++ri]=i,vis[i]=;
    while(ri>=le){
      int x=q[le];
      le++;
      k--;
      ans=max(ans,vis[x]);
      if(!k)break;
      for(i=head[x];i;i=nxt[i]){
          if(du[to[i]]<=)continue;
          du[to[i]]--;
          vis[to[i]]=max(vis[to[i]],vis[x]+);
          if(du[to[i]]==)q[++ri]=to[i];
      }
    }
    printf("%d\n",ans);
    return ;
}