topo,WA 4#,求调

#include<bits/stdc++.h>
using namespace std;
const int N=1e5+5;
int n,k,u,v,d[N],topo[N],vis[N],ans;
vector<int>e[N];
int main(){
    cin>>n>>k;
    int K=n-k;
    for(int i=1;i<n;i++){
        cin>>u>>v;
        e[u].push_back(v);
        e[v].push_back(u);
        topo[u]++;
        topo[v]++;
    }
    queue<int>q;
    for(int i=1;i<=n;i++){
        if(topo[i]==1&&K>=1){
            q.push(i);
            K--;
            vis[i]=1;
            ans=1;
            d[i]=1;
        }
    }
    if(K){
        while(!q.empty()){
            int len=q.size();
            while(len--){
                int u=q.front();
                q.pop();
                for(int i=0;i<e[u].size();i++){
                    int v=e[u][i];
                    if(!vis[v]){
                        vis[v]=1;
                        d[v]=d[u]+1;
                        topo[v]--;
                        if(topo[v]==1)q.push(v),K--;
                        ans=max(ans,d[v]);
                        if(k<1){
                            cout<<ans;
                            return 0;
                        }
                    }
                }
            }
        }
    }
    cout<<ans;
    return 0;
}