#include <bits/stdc++.h> using namespace std; const int N = 3e5+5; int n, a, b; int E[N], par[N], block[N], dp[N]; vector<int> g[N]; void dfs(int u, int p) { par[u] = p; for(int v : g[u]) if(v != p) dfs(u ^ E[v], v); } int process(int u, int p) { dp[u] = 0; vector<int> child; for(int v : g[u]) if(v != p && !block[v]) child.emplace_back(process(E[v] ^ u, v)); sort(child.begin(), child.end(), greater<int>()); for(int i = 0; i < child.size(); i++) dp[u] = max(dp[u], 1 + i + child[i]); return dp[u]; } int main() { scanf("%d %d %d", &n, &a, &b); for(int i = 1, a, b; i < n; i++) { scanf("%d %d", &a, &b); g[a].emplace_back(i), g[b].emplace_back(i); E[i] = a ^ b; } dfs(b, 0); vector<int> vec; int now = a; while(now != b) { vec.emplace_back(par[now]); now ^= E[par[now]]; } int l = 0, r = vec.size() - 1; int ans = 1e9; while(l <= r) { int mid = (l + r) >> 1; block[vec[mid]] = 1; int t_a = process(a, 0), t_b = process(b, 0); block[vec[mid]] = 0; ans = min(ans, max(t_a, t_b)); if(t_a == t_b) break; else if(t_a < t_b) l = mid + 1; else r = mid - 1; } printf("%d\n", ans); return 0; }

torrent.cpp: In function 'int process(int, int)':
torrent.cpp:23:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i = 0; i < child.size(); i++)
                    ~~^~~~~~~~~~~~~~
torrent.cpp: In function 'int main()':
torrent.cpp:29:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d %d %d", &n, &a, &b);
     ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
torrent.cpp:31:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         scanf("%d %d", &a, &b);
         ~~~~~^~~~~~~~~~~~~~~~~