Submission #383338

#	Time	Username	Problem	Language	Result	Execution time	Memory
383338		Aryan_Raina	Race (IOI11_race)	C++14	0 / 100	10 ms	13036 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];
vector<int> length(MXK, INF), lastcnt(MXK, -1);
vector<bool> dead(MXK, false);
int n, k, ans = INT_MAX, cnt = 0;
int OneCentroid(int rt) {
	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)> 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, 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 && (lastcnt[dist] == -1 || len < length[dist])) 
		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);
}

void decompose(int start) {
	int cen = OneCentroid(start);
	length[0] = 0; lastcnt[0] = ++cnt;
	// 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);
	}
	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: 0 / 9
• Subtask 2: 0 / 12
• Subtask 3: 0 / 22
• Subtask 4: 0 / 57