Submission #1188841

#	Time	Username	Problem	Language	Result	Execution time	Memory
1188841		g4yuhg	Race (IOI11_race)	C++20	100 / 100	1154 ms	44944 KiB

race

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

typedef long long ll;
#define fi first
#define se second
#define pii pair<ll,ll>

const int N = 200005;
const int inf = 1e9;

ll del[N], d[N], ans, child[N];
vector<pii> adj[N];
map<ll, ll> mp;
int n, k;

void cnt_child(ll u, ll parent) {
	child[u] = 1;
	for (auto v : adj[u]) {
		if (v.fi == parent || del[v.fi]) continue;
		cnt_child(v.fi, u);
		child[u] += child[v.fi];
	}
}

ll centroid(ll u, ll parent, ll n) {
	for (auto v : adj[u]) {
		if (v.fi == parent || del[v.fi]) continue;
		if (child[v.fi] > n / 2) {
			return centroid(v.fi, u, n);
		}
	}
	return u;
}

void dfs(ll u, ll parent, ll dep) {
	if (mp.find(k - d[u]) != mp.end()) {
		ans = min(ans, dep + mp[k - d[u]]);
	}
	if (d[u] == k) ans = min(ans, dep);
	for (auto v : adj[u]) {
		if (v.fi == parent || del[v.fi]) continue;
		d[v.fi] = d[u] + v.se;
		if (d[v.fi] > k) continue;
		dfs(v.fi, u, dep + 1);
	}
}

void dfs2(ll u, ll parent, ll dep) {
	if (mp.find(d[u]) == mp.end()) {
		mp[d[u]] = dep;
	}
	else {
		mp[d[u]] = min(mp[d[u]], dep);
	}
	for (auto v : adj[u]) {
		if (v.fi == parent || del[v.fi]) continue;
		d[v.fi] = d[u] + v.se;
		if (d[v.fi] > k) continue;
		dfs2(v.fi, u, dep + 1);
	}
}

void gq(ll x) {
	mp.clear();
	d[x] = 0;
	for (auto v : adj[x]) {
		if (del[v.fi]) continue;
		d[v.fi] = d[x] + v.se;
		dfs(v.fi, x, 1);
		dfs2(v.fi, x, 1);
	}
}

void solve(ll u) {
	cnt_child(u, u);
	ll x = centroid(u, u, child[u]);
	gq(x);
	del[x] = 1;
	for (auto v : adj[x]) {
		if (del[v.fi]) continue;
		solve(v.fi);
	}
}

int best_path(int N_input, int K_input, int H[][2], int L[]) {
	n = N_input;
	k = K_input;

	// reset global data
	for (int i = 0; i <= n; i++) {
		adj[i].clear();
		del[i] = d[i] = child[i] = 0;
	}
	ans = inf;

	// build tree
	for (int i = 0; i < n - 1; i++) {
		int u = H[i][0] + 1;
		int v = H[i][1] + 1;
		int w = L[i];
		adj[u].push_back({v, w});
		adj[v].push_back({u, w});
	}

	solve(1);
	if (ans == inf) return -1;
	return ans;
}

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