POJ 3107 Godfather (树重心)

题目链接：http://poj.org/problem?id=3107

题意:

        数重心，并按从小到大输出。

思路:

        dfs

#include <iostream>
#include <cstdio>
#include <cstring>
#include <vector>
using namespace std;
const int N = 5e4 + 5;
struct Edge {
    int next, to;
}edge[N << 1];
vector <int> G[N];
int dp[N], n, head[N], cnt;

inline void add(int u, int v) {
    edge[cnt].next = head[u];
    edge[cnt].to = v;
    head[u] = cnt++;
}

int dfs(int u, int p) {
    dp[u] = 0;
    int sum = 0;
    for(int i = head[u]; ~i; i = edge[i].next) {
        int v = edge[i].to;
        if(v == p)
            continue;
        int temp = dfs(v, u);
        dp[u] = max(dp[u], temp);
        sum += temp;
    }
    dp[u] = max(dp[u], n - sum - 1);
    return sum + 1;
}

int main()
{
    while(~scanf("%d", &n)) {
        for(int i = 1; i <= n; ++i) {
            head[i] = -1;
        }
        cnt = 0;
        for(int i = 1; i < n; ++i) {
            int u, v;
            scanf("%d %d", &u, &v);
            add(u, v);
            add(v, u);
        }
        dfs(1, -1);
        int Max = n;
        vector <int> ans;
        for(int i = 1; i <= n; ++i) {
            Max = min(Max, dp[i]);
        }
        for(int i = 1; i <= n; ++i) {
            if(Max == dp[i]) {
                ans.push_back(i);
            }
        }
        for(int i = 0; i < ans.size(); ++i) {
            if(i == ans.size() - 1) {
                printf("%d
", ans[i]);
            } else {
                printf("%d ", ans[i]);
            }
        }
    }
    return 0;
}