agc001_c题解

水的炸天，不做解释自己看吧

#include<bits/stdc++.h>
#define MAXN 2010
#define inf 0x3f3f3f3f
#define int long long
using namespace std;
namespace SHuxinn{
	struct node {
	    int lst;
		int dep;
		int nxt ;
	} tree[MAXN * 4];
	int n , k , cnt , ans;
	int dfs(int x , int fa , int dis) {
	    int ans = 0;
	    for (int i = tree[x].lst ; i ; i = tree[i].nxt) {
	    	if (tree[i].dep != fa){
	    		ans += dfs(tree[i].dep , x , dis + 1);
			}
			
		}
	    if(dis > k) return ans + 1;
	    else return ans;
	}
	void Sx5() {
	    cin >> n >> k;
	    int u , v;
	    for (int i = 1 ; i < n ; i ++) {
			cin >> u >> v;
		    tree[++cnt].dep = u;
		    tree[cnt].nxt = tree[v].lst;
		    tree[v].lst = cnt;
		    tree[++cnt].dep = v;
		    tree[cnt].nxt = tree[u].lst;
		    tree[u].lst = cnt;
	    }
	    ans = inf;
	    if (k % 2 == 0) {
	    	k /= 2;
	        for (int i = 1 ; i <= n ; i ++)
	            ans = min(ans , dfs(i , 0 , 0));
	    } else {
	    	k = (k - 1) / 2;
	        for (int i = 1 ; i <= n ; i ++){
	        	for (int j = tree[i].lst ; j ; j = tree[j].nxt){
	        		if (i < tree[j].dep)
	                    ans = min(ans , dfs(i , tree[j].dep , 0) + dfs(tree[j].dep , i , 0));
				}
	                
			}
	            
	    }
	    cout << ans;
		return;
	}
}
signed main(){
	freopen("tree.in" , "r" , stdin);
	freopen("tree.out" , "w" , stdout);
	SHuxinn::Sx5();
	return 0;
}