Submission #383355

#	Time	Username	Problem	Language	Result	Execution time	Memory
383355		Aryan_Raina	Race (IOI11_race)	C++14	100 / 100	584 ms	38660 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;

const int MXN = 2e5+9, MXK = 1e6+9;
vector<ar<int,2>> g[MXN], to_update;
vector<int> length(MXK, INF), indexes, sz(MXN);
vector<bool> dead(MXK, false);
int n, k, ans = INT_MAX;
int OneCentroid(int rt) {
	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)> cent = [&](int u, int pu) {
		for (auto v : g[u]) if (v[1] != pu && !dead[v[1]]) {
			if (sz[v[1]] > sz[rt]/2) return cent(v[1], u);
		}
		return u;
	};
	return cent(rt, rt);
}

void dfs(int u, int pu, int len, int dist) {
	if (k < dist || len > ans) return;
	if (k-dist >= 0) ans = min(ans, length[k-dist] + len);
	to_update.push_back({dist, len});
	for (auto v : g[u]) if (v[1] != pu && !dead[v[1]]) 
		dfs(v[1], u, len + 1, dist + v[0]);
}
 
void decompose(int start) {
	int cen = OneCentroid(start);
	length[0] = 0; indexes.push_back(0);
	// 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]);
		for (auto x : to_update) if (x[0] <= k) {
			if (length[x[0]] >= INF/2) indexes.push_back(x[0]);
			length[x[0]] = min(length[x[0]], x[1]);
		}
		to_update.clear();
	}
	for (int i : indexes) length[i] = INF;
	indexes.clear();

	dead[cen] = true;
	for (auto v : g[cen]) if (!dead[v[1]]) decompose(v[1]);
	dead[cen] = false;
}
 
int best_path(int N, int K, int H[][2], int L[]) {
	n = N, k = K;
	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]});
	}
  	decompose(0);
	return (ans < INF/2) ? ans : -1;
}
 

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