【HDU 6228、2017ACM/ICPC亚洲区沈阳站】Tree

只要能将题目转化成找关键边即可。

#include <cstdio>#include <cstring>#include <algorithm>#include <vector>using namespace std;#define N 200003int cnt[N], n, k, ans;vector<int> V[N];void dfs(int u, int f) {    int i, v;    cnt[u] = 1;    for (i = 0;i < V[u].size();i++) {        v = V[u][i];        if (v == f) continue;        dfs(v, u);        cnt[u] += cnt[v];        if (cnt[v] >= k && n-cnt[v] >= k) ans++;    }}int main() {    int T, u, v, i;    scanf("%d", &T);    while (T--) {        scanf("%d%d", &n, &k);        for (i = 1;i <= n;i++) V[i].clear();        for (i = 1;i < n;i++) {            scanf("%d%d", &u, &v);            V[u].push_back(v);            V[v].push_back(u);        }        ans = 0;        memset(cnt, 0, sizeof(cnt));        dfs(1, 0);        printf("%d\n", ans);    }}