Submission #383294

#	Time	Username	Problem	Language	Result	Execution time	Memory
383294		Aryan_Raina	Race (IOI11_race)	C++14	21 / 100	3073 ms	8044 KiB

race

#include "race.h"
#include <bits/stdc++.h>
using namespace std;

#define ll long long
#define ld long double
#define ar array

const int INF = 1e9;
const int MOD = 1e9 + 7;

int OneCentroid(int rt, vector<vector<ar<int,2>>> &g, vector<bool> &dead) {
	int n = g.size();
	vector<int> sz(n);
	function<void(int,int)> get_sz = [&](int u, int pu) {
		sz[u] = 1;
		for (auto v : g[u]) if (v[1] != pu && !dead[v[1]]) {
			get_sz(v[1], u);
			sz[u] += sz[v[1]];
		}
	};
	get_sz(rt, rt);
	function<int(int,int)> dfs = [&](int u, int pu) {
		for (auto v : g[u]) if (v[1] != pu && !dead[v[1]]) {
			if (sz[v[1]] > sz[rt]/2) return dfs(v[1], u);
		}
		return u;
	};
	return dfs(rt, rt);
}

int CentroidDecomposition(vector<vector<ar<int,2>>> &g, int k) {
	int n = g.size();
	vector<bool> dead(n, false);
	vector<int> length(k+1, INF), lastcnt(k+1, -1);
	vector<ar<int,2>> to_update;
	int ans = INT_MAX; int cnt = 0;
	function<void(int,int,int,int,bool)> dfs = [&](int u, int pu, int len, int dist, bool update) {
		if (k < dist || len > ans) return;
		if (!update && k-dist >= 0 && lastcnt[k-dist] == cnt)
			ans = min(ans, length[k-dist] + len);
		if (update) {
			if (lastcnt[dist] != cnt || length[dist] > len) length[dist] = len; 
			lastcnt[dist] = cnt;
		}
		for (auto v : g[u]) if (v[1] != pu && !dead[v[1]]) 
			dfs(v[1], u, len + 1, dist + v[0], update);
	};
	function<void(int)> decompose = [&](int start) {
		int cen = OneCentroid(start, g, dead);
		dead[cen] = true;
		length[0] = 0; lastcnt[0] = ++cnt;
		// do stuff with subtree of centroid here
		// get length, distance to each node in subtree of centroid from centroid
		// ans = min(ans, length) if distance corresponding to it is k
		for (auto v : g[cen]) if (!dead[v[1]]) {
			dfs(v[1], cen, 1, v[0], false);
			dfs(v[1], cen, 1, v[0], true);
		}
		for (auto v : g[cen]) if (!dead[v[1]]) decompose(v[1]);
		dead[cen] = false;
	};
	decompose(0);
	return (ans < INF/2) ? ans : -1;
}

int best_path(int N, int K, int H[][2], int L[]) {
	vector<vector<ar<int,2>>> g(N);
	for (int i = 0; i < N-1; i++) {
		g[H[i][0]].push_back({L[i], H[i][1]});
		g[H[i][1]].push_back({L[i], H[i][0]});
	}
  	return CentroidDecomposition(g, K);
}

• Subtask 1: 9 / 9
• Subtask 2: 12 / 12
• Subtask 3: 0 / 22
• Subtask 4: 0 / 57