結果

問題 No.1976 Cut then Connect
コンテスト
ユーザー kwm_t
提出日時 2022-06-12 14:44:06
言語 C++17
(gcc 13.3.0 + boost 1.87.0)
結果
WA  
実行時間 -
コード長 4,007 bytes
コンパイル時間 2,412 ms
コンパイル使用メモリ 210,404 KB
最終ジャッジ日時 2025-01-29 20:49:39
ジャッジサーバーID
（参考情報） 		judge3 / judge5
このコードへのチャレンジ
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ファイルパターン 結果
sample WA * 2
other WA * 31
権限があれば一括ダウンロードができます

ソースコード

diff # 

#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
//using namespace atcoder;
//using mint = modint1000000007;
//const int mod = 1000000007;
//using mint = modint998244353;
//const int mod = 998244353;
const int INF = 1e9;
//const long long LINF = 1e18;
//const bool debug = false;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n-1); i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r-1);i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define endl "\n"
#define P pair<long long,long long>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }
struct ReRooting {
	struct Edge {
		int to;
		Edge(int _to) :to(_to) {}
	};
	struct Data {
		int diameter;	//直径
		int rootmax1st;	//根からのmax
		int rootmax2nd;	//根からの2ndmax
		Data() :diameter(0), rootmax1st(0), rootmax2nd(0) {}
		Data(int _diameter, int _rootmax1st, int _rootmax2nd) :diameter(_diameter), rootmax1st(_rootmax1st), rootmax2nd(_rootmax2nd) {}
	};
	vector<vector<Edge>>g;
	vector<Data>dp;
	int ans;
	int sz;
	ReRooting(int _sz) :sz(_sz) {
		g.resize(sz);
		dp.reserve(sz);
	}
	void ReadGraph() {
		rep(i, sz - 1) {
			int a, b; cin >> a >> b; a--; b--;
			g[a].push_back({ b });
			g[b].push_back({ a });
		}
	}
	Data  merge(const Data &lh, const Data &rh) {
		Data ret = lh;
		chmax(ret.diameter, rh.diameter);
		chmax(ret.diameter, rh.rootmax1st + 1);
		if (rh.rootmax1st + 1 >= ret.rootmax1st) {
			ret.rootmax2nd = ret.rootmax1st;
			ret.rootmax1st = rh.rootmax1st + 1;
		}
		else if (rh.rootmax1st + 1 >= ret.rootmax2nd) {
			ret.rootmax2nd = rh.rootmax1st + 1;
		}
		chmax(ret.diameter, ret.rootmax1st + ret.rootmax2nd);
		return ret;
	}
	Data  mergeSub(const Data &lh, const Data &rh) {//★★
		Data ret;
		ret.diameter = max(lh.diameter, rh.diameter);
		chmax(ret.diameter, lh.rootmax1st + rh.rootmax1st);
		vector<int>v = { lh.rootmax1st,lh.rootmax2nd,rh.rootmax1st,rh.rootmax2nd };
		sort(allR(v));
		ret.rootmax1st = v[0];
		ret.rootmax2nd = v[1];
		//cout << lh.diameter << lh.rootmax1st << lh.rootmax2nd << endl;
		//cout << rh.diameter << rh.rootmax1st << rh.rootmax2nd << endl;
		//Data ret = lh;
		//ret.val *= rh.val;
		return ret;
	}
	void dfs(int v, int p = -1) {
		Data val;
		for (auto e : g[v]) {
			if (p == e.to)continue;
			dfs(e.to, v);
			val = merge(val, dp[e.to]);
		}
		dp[v] = val;
	}
	void dfsR(int v, int p = -1) {
		if (-1 != p) {
			Data data = dp[p];
			int anssub = 0;
			chmax(anssub, data.diameter);
			chmax(anssub, dp[v].diameter);
			chmax(anssub, 1 + (dp[v].diameter + 1) / 2 + (data.diameter + 1) / 2);
			chmin(ans, anssub);
			//cout << v << endl;
			//cout << "child " << dp[v].diameter << endl;
			//cout << "head " << dp[p].diameter << " " << dp[p].rootmax1st << " " << dp[p].rootmax2nd << endl;
			//cout << "child " << dp[v].diameter << " " << dp[v].rootmax1st << " " << dp[v].rootmax2nd << endl;
			//cout << anssub << endl;
			//cout << endl;
		}
		vector<Data>vdata;
		for (auto e : g[v]) vdata.push_back(dp[e.to]);
		int sz = vdata.size();
		vector<Data>sumL(sz + 1), sumR(sz + 1);
		rep(i, sz)sumL[i + 1] = merge(sumL[i], vdata[i]);
		rep(i, sz)sumR[i + 1] = merge(sumR[i], vdata[sz - i - 1]);
		for (int i = 0; i < g[v].size(); ++i) {
			auto e = g[v][i];
			if (p == e.to)continue;
			dp[v] = mergeSub(sumL[i], sumR[sz - (i + 1)]);
			dfsR(e.to, v);
		}
	}
	void output() {
		cout << ans << endl;
	}
	void debug() {
		rep(i, sz)cout << dp[i].diameter << " " << dp[i].rootmax1st << " " << dp[i].rootmax2nd << endl;
	}
	void solve() {
		ans = INF;
		ReadGraph();
		dfs(0);
		debug();
		dfsR(0);
		output();
	}
};
int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int n; cin >> n;
	ReRooting reroot(n);
	reroot.solve();
	return 0;
}
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