搜索与图论：树的重心

题目描述

输入样例

9
1 2
1 7
1 4
2 8
2 5
4 3
3 9
4 6

输出样例

4

参考代码

#include <cstring>
#include <iostream>
#include <algorithm>using namespace std;const int N = 100010, M = N * 2;int n, m;
int h[N], e[M], ne[M], idx;
bool st[N];int ans = N;void add(int a, int b)
{e[idx] = b, ne[idx] = h[a], h[a] = idx++;
}// 以u为根的子树中点的数量
int dfs(int u)
{st[u] = true;   // 标记一下，已经被搜过了int sum = 1, res = 0;for (int i = h[u]; i != -1; i = ne[i]){int j = e[i];if (!st[j]){int s = dfs(j);res = max(res, s);sum += s;}}res = max(res, n - sum);ans = min(ans, res);return sum;
}int main()
{   cin >> n >> m;memset(h, -1, sizeof h);for (int i = 0; i < n; i++){int a, b;cin >> a >> b;add(a, b), add(b, a);}dfs(1);cout << ans << endl;return 0;
}