#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define inf 0x3f3f3f3f
const int mx = 2e5+100;
vector<int>ve[mx];
int so[mx], sou[mx], sum[mx], n, h[mx];
int ff[mx];
void solve(int x, int u, int y) {
while (x != u && so[u]-so[x] > so[x]) {
x = ff[x];
}
while (y != u && so[u]-so[y] > so[y]) {
y = ff[y];
}
if (h[x] > h[y]) sou[u] = x;
else sou[u] = y;
return;
}
void dfs1(int u, int fa) {
sou[u] = u;
so[u] = 1, ff[u] = fa;
for (int i = 0; i < ve[u].size(); ++i) {
int v = ve[u][i];
if (v == fa) continue;
h[v] = h[u]+1;
dfs1(v, u);
so[u] += so[v];
solve(sou[u], u, sou[v]);
}
}
int main(){
int u, v;
scanf("%d", &n);
for (int i = 1; i < n; ++i) {
scanf("%d%d", &u, &v);
ve[u].push_back(v);
ve[v].push_back(u);
}
dfs1(1, 0);
for (int i = 1; i <= n; ++i) {
int a = sou[i], b = -1;
if (sou[i] != i) {
// printf("%d %d\n", so[i]-so[sou[i]]-1, so[ff[sou[i]]]);
if (so[i]-so[sou[i]] == so[sou[i]]) b = ff[sou[i]];
if (b != -1) {
if (a > b) swap(a, b);
}
}
printf("%d", a);
if (b != -1) printf(" %d", b);
puts("");
}
}
徐州 icpc 区域赛 M. Kill the tree 树的重心
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转载自blog.csdn.net/ClonH/article/details/103486563
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