POJ 3107 Godfather (树的重心模板题)

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题意：给出一棵树，求出所有树的重心，并且按编号从小到大输出。

直接套模板即可。

代码如下：

#include<iostream>
#include<cstdio>
#include<vector>
#include<queue>
#include<utility>
#include<stack>
#include<algorithm>
#include<cstring>
#include<string>
#include<cmath>
#include<set>
#include<map>
using namespace std;
const int maxn = 5e4 + 5;
int head[maxn], to[maxn << 1], nx[maxn << 1], tot;
bool vst[maxn];
int Min = 0x3f3f3f3f, key;
int cnt[maxn], n;
vector <int> vec;

void add_edge(int u, int v) {
to[tot] = v, nx[tot] = head[u], head[u] = tot++;
swap(u, v);
to[tot] = v, nx[tot] = head[u], head[u] = tot++;
}

int dfs(int u, int par) {
cnt[u] = 1;
int Max = 0;
for(int i = head[u]; ~i; i = nx[i]) {
int v = to[i];
if(v != par) {
cnt[u] += dfs(v, u);
Max = max(Max, cnt[v]);
}
}
if(Max < n - cnt[u])
Max = n - cnt[u];
if(Max < Min) {
vec.clear();
Min = Max;
vec.push_back(u);
} else if(Max == Min) {
vec.push_back(u);
}
return cnt[u];
}

int main() {
#ifndef ONLINE_JUDGE
// freopen("in.txt", "r", stdin);
// freopen("out.txt", "w", stdout);
#endif
memset(head, -1, sizeof(head));
tot = 0;
Min = 0x3f3f3f3f;
scanf("%d", &n);
for(int i = 1, u, v; i < n; i++) {
scanf("%d%d", &u, &v);
add_edge(u, v);
}
dfs(1, 1);
sort(vec.begin(), vec.end());
for(int i = 0; i < vec.size(); i++)
printf("%d%c", vec[i], i + 1 == vec.size() ? '\n' : ' ');
return 0;
}