51NOD1378 树形DP + 贪心

#include <bits/stdc++.h>

using namespace std;

const int maxn = 1e5+10;
int dp[maxn];
vector <int> V[maxn];
int N,K;
int vis[maxn];

int dfs(int n)
{
    static int ans = 0;
    int Min = maxn;
    int Max = -maxn;
    //vis[n] = true;
    int len = V[n].size();
    for(int i=0;i<len;i++){
        //if(!vis[V[n][i]]){
            dfs(V[n][i]);
            Min = min(Min,dp[V[n][i]]);
            Max = max(Max,dp[V[n][i]]);
        //}
    }
    if(Min == maxn){
        dp[n] = -1;
    }
    else if(Min <= -K){
        ++ans;
        dp[n] = K;
    }
    else if(Min + Max > 0){
        dp[n] = Max - 1;
    }
    else{
        dp[n] = Min - 1;
    }
    return ans;
}

int main()
{
    ios::sync_with_stdio(false);
    cin>>N>>K;
    for(int i=1;i<N;i++) {
        int s,e;
        cin>>s>>e;
        V[s].push_back(e);
        V[e].push_back(s);
    }
    if(!K){
        cout<< N <<endl;
        return 0;
    }
    int ans = dfs(0);
    cout<< (dp[0] < 0 ? ans+1 : ans) <<endl;
    return 0;
}

/***
4 1
0 1
0 2
0 3

5 1
0 1
0 2
0 3
3 4
***/