HDU5326多校签到题，搜索子孙节点，

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dfs一发即可：

#include <bits/stdc++.h>using namespace std;const int N = 110;vector<int> E[N];int in[N], son[N];bool vis[N];void dfs(int u){    vis[u] = true;    son[u] = 1;    for(int v: E[u]) {        dfs(v);        son[u] += son[v];    }}int main(){    freopen("in.txt", "r", stdin);    freopen("out.txt", "w", stdout);    int n, k, a, b;    while(scanf("%d%d", &n, &k) == 2) {        memset(vis, false, sizeof(vis));        memset(in, 0, sizeof(in));        for(int i = 0; i < n; i++) {            E[i].clear();        }        for(int i = 1; i < n; i++) {            scanf("%d%d", &a, &b);            assert(1 <= a && a <= n);            assert(1 <= b && b <= n);            a--; b--;            E[a].push_back(b);            in[b]++;        }        int root = -1;        for(int i = 0; i < n; i++) if(!in[i]) {            root = i;        }        assert(root == 0);        dfs(root);        for(int i = 0 ; i < n; i++) if(!vis[i]) {            while(1);        }        int ret = 0;        for(int i = 0; i < n; i++) if(son[i] - 1 == k) {            ret ++;        }        printf("%d\n", ret);    }    return 0;}

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