Submission #100703

#	Time	Username	Problem	Language	Result	Execution time	Memory
100703		arman_ferdous	Race (IOI11_race)	C++17	43 / 100	3099 ms	27100 KiB

race

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

using ll = long long;
const int N = 2e5+10;
const int MAX = 1e6+10;

int n, k;
vector< pair<int,int> > g[200010];

int sub[N];
bool Deleted[N];

void dfs(int u, int f) {
	sub[u] = 1;
	for(auto it : g[u]) if(it.first != f && !Deleted[it.first]) {
		dfs(it.first, u);
		sub[u] += sub[it.first];
	}
}

int get_centroid(int u, int f, int lim) {
	int ret = -1;
	for(auto it : g[u]) if(it.first != f && !Deleted[it.first]) {
		if(sub[it.first] * 2 > lim) {
			ret = get_centroid(it.first, u, lim);
			break;
		}
	} if(ret == -1) return u;
	return ret;
}

int F[MAX];
int get_subtree(int u, int f, int cost, int cnt) {
	int ret = N + N;
	if(cost <= k) ret = F[k - cost] + cnt;
	if(cost == k) ret = min(ret, cnt);

	for(auto it : g[u]) if(it.first != f && !Deleted[it.first] && cost + it.second <= k)
		ret = min(ret, get_subtree(it.first, u, cost + it.second, cnt + 1));
	return ret;
}

void upd_subtree(int u, int f, int cost, int cnt) {
	if(cost < MAX) F[cost] = min(F[cost], cnt);
	for(auto it : g[u]) if(it.first != f && !Deleted[it.first] && cost + it.second <= k)
		upd_subtree(it.first, u, cost + it.second, cnt + 1);
}

int calc(int u) {
	for(int i = 0; i <= k; i++) F[i] = N+N;

	int ans = N + N;
	for(auto it : g[u]) if(!Deleted[it.first]) {
		ans = min(ans, get_subtree(it.first, u, it.second, 1));
		upd_subtree(it.first, u, it.second, 1);
	} return ans;
}

int solve(int s) {
	dfs(s,-1);
	int u = get_centroid(s, -1, sub[s]);
	int ret = calc(u);
	Deleted[u] = true;
	for(auto it : g[u]) if(!Deleted[it.first])
		ret = min(ret, solve(it.first));
	return ret;
}

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({H[i][1], L[i]});
		g[H[i][1]].push_back({H[i][0], L[i]});
	}
  	int ans = solve(0);
  	if(ans >= N+N) return -1;
  	return ans;
}

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