F - Distance Sums 2（模板）
#include <bits/stdc++.h>
using namespace std;
int main(){
int n; cin >> n;
vector<vector<int>> g(n);
for(int i = 0; i < n - 1; i++) {
int a, b; cin >> a >> b;
g[a-1].push_back(b-1);
g[b-1].push_back(a-1);
}
vector<long long> sub(n,1), ans(n);
function<void(int, int, int)> dfs=[&](int i, int p, int d){
ans[0] += d;
for(int x : g[i]) if(x != p) {
dfs(x, i, d+1);
sub[i] += sub[x];
}
}; dfs(0, -1, 0);
function<void(int, int)> dfs2=[&](int i, int p){
for(int x : g[i]) if(x != p) {
ans[x] = ans[i] - 2 * sub[x] + n;
dfs2(x, i);
}
}; dfs2(0, -1);
for(long long x : ans) cout << x << endl;
}
思路
ans[v]=ans[u]−size[v]+(N−size[v])
