Codeforces Round #321 (Div. 2) C Kefa and Park（深搜）

dfs一遍，维护当前连续遇到的喵的数量，然后剪枝，每个统计孩子数量判断是不是叶子结点。

#include<bits/stdc++.h>
using namespace std;

const int maxn = 2e5+5;
int a[maxn];
int head[maxn],nxt[maxn<<1],to[maxn<<1],ect;

inline void addEdge(int u,int v)
{
    to[ect] = v;
    nxt[ect] = head[u];
    head[u] = ect++;
}

int ct[maxn],m,cnt;
void dfs(int u,int f)
{
    if(a[u]) ct[u] = ct[f]+1;
    if(ct[u]>m) return;
    int ch = 0;
    for(int i = head[u]; ~i ; i = nxt[i]){
        int v = to[i];
        if(v == f) continue;
        ch++;
        dfs(v,u);
    }
    if(!ch) { cnt++; }
}

//#define LOCAL

int main()
{
#ifdef LOCAL
    freopen("in.txt","r",stdin);
#endif
    memset(head,-1,sizeof(head));
    int n; scanf("%d%d",&n,&m);
    for(int i = 1; i <= n; i++) scanf("%d",a+i);
    for(int i = 1; i < n; i++){
        int u,v; scanf("%d%d",&u,&v);
        addEdge(u,v); addEdge(v,u);
    }
    dfs(1,0);
    printf("%d",cnt);
    return 0;
}