WA on #29，跪求大佬帮助 π π

#include <bits/stdc++.h>
using namespace std;
const int maxn=1e5+10;
int n,k,cnt,root;
struct edge
{
	int to,nxt;
}e[maxn<<1];
int head[maxn],deep[maxn],mxdep[maxn],ans[maxn],f[maxn],numson[maxn];
struct node
{
	int deep,id;
	bool operator < (const node &p) const
	{
		return this->deep<p.deep;
	}
}tmp[maxn];
void add (int u,int v)
{
	cnt++;
	e[cnt].to=v;
	e[cnt].nxt=head[u];
	numson[u]++;
	head[u]=cnt;
}
void dfs (int x,int fa)
{
	f[x]=fa;
	mxdep[x]=deep[x]=deep[fa]+1;
	for (int i=head[x];i;i=e[i].nxt) {
		int son=e[i].to;
		if (son==fa) continue;
		dfs(son,x);
		mxdep[x]=max(mxdep[x],mxdep[son]);
	}
}
void dfs2 (int x,int fa)
{
	mxdep[x]=deep[x]=deep[fa]+1;
	for (int i=head[x];i;i=e[i].nxt) {
		int son=e[i].to;
		if (son==fa) continue;
		dfs2(son,x);
		mxdep[x]=max(mxdep[x],mxdep[son]);
	}
}
int main()
{
	ios_base::sync_with_stdio(false);
	cin.tie(0); cout.tie(0);
	cin>>n>>k;
	for (int i=1;i<n;i++) {
		int u,v;
		cin>>u>>v;
		add(u,v); add(v,u);
	}
//	cout<<"The edge are as below: "<<endl;
//	for (int kk=1;kk<=n;kk++) {
//		for (int i=head[kk];i;i=e[i].nxt)
//			cout<<e[i].to<<" ";
//		cout<<endl;
//	}
	// 注意1不应该是叶子节点
	
	for (int i=1;i<=n;i++)
		if (numson[i]>1) {
			root=i;
//			cout<<"root is "<<root<<endl;
			dfs(i,0);
			break;
		} 
//	cout<<"The deep are as below"<<endl;
//	for (int i=1;i<=n;i++)
//		cout<<deep[i]<<" "<<mxdep[i]<<endl;
	int mx1=0,mx2=0;
	for (int i=head[root];i;i=e[i].nxt) {
		if (mx1<=mxdep[e[i].to]) {
			mx2=mx1;
			mx1=mxdep[e[i].to];
		}
		else if (mx2==0) mx2=mxdep[e[i].to];
	}
	for (int i=1;i<=n;i++) {
		tmp[i].deep=deep[i];
		tmp[i].id=i;
	}
	sort(tmp+1,tmp+1+n);
	int length=mx1+mx2-1;
	root=tmp[n].id;
//	cout<<"length is "<<length<<endl;
	for (int kk=1;kk<=length/2;kk++)
		root=f[root];
	memset(deep,0,sizeof(deep));
//	cout<<"root is "<<root<<endl;
	dfs2(root,0);
//	for (int i=1;i<=n;i++) cout<<deep[i]<<" "<<mxdep[i]<<endl;
	for (int i=1;i<=n;i++)
		ans[i]=mxdep[i]-deep[i];
	sort(ans+1,ans+1+n);
	cout<<ans[n-k]+1;
	return 0;
}
/*
12 2
1 2
1 3
3 4
3 5
5 6
5 7
5 8
7 9
7 10
10 11
10 12
*/