Submission #883892

#TimeUsernameProblemLanguageResultExecution timeMemory
883892GithubTorrent (COI16_torrent)C++14
69 / 100
279 ms38652 KiB
#include <iostream> #include <vector> #include <queue> #include <cstring> #include <map> #include <climits> #include <cmath> #include <algorithm> #include <stack> using namespace std; #define speedup ios_base::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr); #define ll long long vector<vector<int>> graph; void dfs(int u, int p, vector<int>& dp){ if (graph[u].size() == 1){ dp[u] = 0; return; } vector<pair<int, int>> child; for (int v: graph[u]){ if (v != p){ dfs(v, u, dp); child.push_back({dp[v], v}); } } sort(child.begin(), child.end(), greater<pair<int, int>>()); int sz = child.size(); for (int i = 0; i < sz; i++){ dp[u] = max(dp[child[i].second]+i+1, dp[u]); } } void dfs2(int u, int p, vector<int>& time, vector<int>& dp){ vector<pair<int, int>> child; for (int v: graph[u]){ if (v != p){ child.push_back({dp[v], v}); } } sort(child.begin(), child.end(), greater<pair<int, int>>()); int sz = child.size(); for (int i = 0; i < sz; i++){ time[child[i].second] = time[u]+i+1; dfs2(child[i].second, u, time, dp); } } pair<int, int> edge; void dfs3(int u, int p, vector<int>& comp){ for (int v: graph[u]){ if (v != p){ if (comp[u] != comp[v]){ edge = {u, v}; return; } dfs3(v, u, comp); } } } int main(){ int n, a, b; cin >> n >> a >> b; a--, b--; graph.resize(n); for (int i = 0; i < n-1; i++){ int u, v; cin >> u >> v; u--, v--; graph[u].push_back(v); graph[v].push_back(u); } vector<int> dp1(n), dp2(n); dfs(a, -1, dp1); dfs(b, -1, dp2); vector<int> T1(n), T2(n); dfs2(a, -1, T1, dp1); dfs2(b, -1, T2, dp2); vector<int> comp(n); for (int i = 0; i < n; i++){ if (T1[i] < T2[i]){ comp[i] = 1; }else{ comp[i] = 2; } } dfs3(0, -1, comp); auto it1 = find(graph[edge.first].begin(), graph[edge.first].end(), edge.second); auto it2 = find(graph[edge.second].begin(), graph[edge.second].end(), edge.first); graph[edge.first].erase(it1); graph[edge.second].erase(it2); dp1.clear(), dp2.clear(), T1.clear(), T2.clear(); dp1.resize(n); dp2.resize(n), T1.resize(n), T2.resize(n); dfs(a, -1, dp1); dfs(b, -1, dp2); dfs2(a, -1, T1, dp1); dfs2(b, -1, T2, dp2); int ans = 0; for (int i = 0; i < n; i++){ if (comp[i] == 1) { ans = max(ans, T1[i]); }else{ ans = max(ans, T2[i]); } } cout << ans << endl; return 0; }
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