55 lines
1.2 KiB
C++
55 lines
1.2 KiB
C++
#include <bits/stdc++.h>
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using namespace std;
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const int MAXN = 1e5 + 5;
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//dep[u]代表u的深度
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//leaf[u]代表以u为根的子树中，深度最浅的那个叶子节点的深度。
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int n , m , rt , leaf[MAXN] , dep[MAXN];
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vector<int> graph[MAXN];
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// 算出dep[u]和leaf[u]
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int dfs(int u, int fa) { // 返回距离u点最近的叶子节点深度
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dep[u] = dep[fa] + 1;
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// u是叶子节点
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if(graph[u].size()==1) {
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leaf[u] = dep[u];
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return leaf[u];
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}
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for(int v : graph[u]) {
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if(v == fa) continue;
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leaf[u] = min(dfs(v , u) , leaf[u]);
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}
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return leaf[u];
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}
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// 节点u能够被控制所需的farmer数量
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int dfs2(int u, int fa) {
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if(dep[u] - 1 >= leaf[u] - dep[u]) return 1;
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int cnt = 0;
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for (int v : graph[u]) {
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if (v == fa) continue;
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cnt += dfs2(v, u);
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}
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return cnt;
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}
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int main() {
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// freopen("atlarge.in", "r", stdin);
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// freopen("atlarge.out", "w", stdout);
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memset(leaf , 0x3f , sizeof(leaf));
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scanf("%d%d" , &n, &rt);
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for(int i = 0; i < n - 1 ; i++) {
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int u, v;
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scanf("%d%d" , &u , &v);
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graph[u].push_back(v);
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graph[v].push_back(u);
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}
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dfs(rt , 0);
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printf("%d\n" , dfs2(rt, 0));
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return 0;
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}
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