ACdream 1015 Double Kings 树的重心

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思路：删除根结点，其最大子树的节点最少。求一次树的重心即可。

AC代码

#include <cstdio>#include <cmath>#include <cctype>#include <algorithm>#include <cstring>#include <utility>#include <string>#include <iostream>#include <map>#include <set>#include <vector>#include <queue>#include <stack>using namespace std;#pragma comment(linker, "/STACK:1024000000,1024000000") #define eps 1e-10#define inf 0x3f3f3f3f#define PI pair<int, int> typedef long long LL;const int maxn = 5e4 + 5;vector<int>G[maxn];int ans, n;int dfs(int u, int pre) {int cnt = 0, maxt = 0;for(int i = 0; i < G[u].size(); ++i) {int v = G[u][i];if(v == pre) continue;int d = dfs(v, u);cnt += d;maxt = max(maxt, d);}maxt = max(maxt, n - cnt - 1);ans = min(ans, maxt);return cnt + 1;}int main() {while(scanf("%d", &n) == 1) {for(int i = 1; i <= n; ++i) G[i].clear();int u, v;for(int i = 0; i < n-1; ++i) {scanf("%d%d", &u, &v);G[u].push_back(v);G[v].push_back(u);}ans = inf;dfs(1, -1);printf("%d\n", n - ans);}return 0;}

如有不当之处欢迎指出！

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