POJ #3107. 教父

題意

求一棵樹的多個重心並按照字典序輸出

題解

求樹的重心

調試記錄

無

#include <cstdio>
#include <algorithm>

#define maxn 500005
#define INF 0x3f3f3f3f

using namespace std;

int first[maxn], next[maxn * 2];
int to[maxn * 2], tot = 0;
int size[maxn], ans[maxn], n, min_max_subtree = INF;/*1*/ 

void AddEdge(int x, int y){
	++tot;
	to[tot] = y;
	next[tot] = first[x];
	first[x] = tot;
}

void FindCentre(int x, int parent){
	size[x] = 1;
	int max_subtree = 0;
	for (int i = first[x]; i; i = next[i]){
		if (to[i] != parent){
			FindCentre(to[i],x);
			size[x] += size[to[i]];
			max_subtree = max(max_subtree, size[to[i]]);
		}
	}
	max_subtree = max(max_subtree, n-size[x]);
	if (max_subtree < min_max_subtree){
		min_max_subtree = max_subtree;
		ans[0] = 0;
		ans[++ans[0]] = x;
	}
	else if (max_subtree == min_max_subtree) ans[++ans[0]] = x;
} 

int main(){
	scanf("%d", &n);
	
	for (int x, y, i = 1; i <= n - 1; i++){
		scanf("%d%d", &x, &y);
		AddEdge(x, y); AddEdge(y, x);
	}	
	
	FindCentre(1, 0);
	
	sort(ans + 1, ans + ans[0] + 1);
	for (int i = 1; i <= ans[0]; i++) printf("%d ", ans[i]);
	printf("\n");
	
	return 0;
}
//http://poj.org/problem?id=3107