Submission #114450

#	Time	Username	Problem	Language	Result	Execution time	Memory
114450		mosesmayer	Race (IOI11_race)	C++17	100 / 100	414 ms	60620 KiB

race

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include "race.h"
#define fi first
#define se second
using namespace std;
using namespace __gnu_pbds;
typedef vector<int> vi;
typedef pair<int,int> pii;

const int MXN = 1e6;
const int mxsz = 2e5 + 3;
int n, k;
vector<pii> adj[mxsz];

int sz[mxsz], dep[mxsz], bc[mxsz], in[mxsz], out[mxsz], flat[mxsz];
long long dist[mxsz];
gp_hash_table<long long, int> sack;

void getsz(int u, int prv = -1){
	static int tme = 0;
	in[u] = ++tme; flat[tme] = u;
	sz[u] = 1;
	for (int i = 0, nx, w; i < adj[u].size(); i++){
		nx = adj[u][i].fi; w = adj[u][i].se;
		if (nx == prv) continue;
		dep[nx] = dep[u] + 1;
		dist[nx] = dist[u] + w;
		getsz(nx, u);
		sz[u] += sz[nx];
		if (bc[u] == -1 || sz[nx] > sz[bc[u]]) bc[u] = nx;
	}
	out[u] = tme;
}

int ans = 0x3f3f3f3f;

void dfs(int u, int prv, bool keep){
	for (int i = 0, nx; i < adj[u].size(); i++){
		nx = adj[u][i].fi;
		if (nx == prv || nx == bc[u]) continue;
		dfs(nx, u, 0);
	}
	if (bc[u] != -1) dfs(bc[u], u, 1);
//	cout << " begin calc " << u << ' ' << dist[u] << '\n';
	sack[dist[u]] = u;
	if (bc[u] != -1){
//		cout << "try big:\n";
		long long w = k + dist[u];
		if (sack.find(w) != sack.end()){
//			cout << "found " <<sack[w] << '\n';
			ans = min(ans, dep[sack[w]] - dep[u]);
		}
	}
	for (int i = 0, nx, w; i < adj[u].size(); i++){
		nx = adj[u][i].fi;
		if (nx == prv || nx == bc[u]) continue;
		for (int j = in[nx]; j <= out[nx]; j++){
			int x = flat[j];
			long long w = dist[x] - dist[u] - dist[u];
			w = 1LL * k - w;
//			cout << "from " << x << " dist " << w << '\n';
			if (sack.find(w) != sack.end()){
				int y = sack[w];
//				cout << "found " << y << '\n';
				ans = min(ans, dep[x] + dep[y] - 2 * dep[u]);
			}
		}
		for (int j = in[nx]; j <= out[nx]; j++){
			int x = flat[j];
			long long w = dist[x];
//			cout << " insert " << x << ' ' << w << '\n';
			if (sack.find(w) == sack.end()
					|| dep[x] < dep[sack[w]]) sack[w] = x;
		}
	}
//	for (int i = 0; i <= k; i++) cout << sack[i] << " \n"[i==k];
//	for (int i = in[u]; i <= out[u]; i++){
//		int x = flat[i];
//		long long w = dist[x] - dist[u] - dist[u];
//		w = 1LL * k - w;
//		cout << "from " << x << " dist " << w << '\n';
//		if (sack.find(w) != sack.end()){
//			int y = sack[w];
//			cout << "found " << y << '\n';
//			ans = min(ans, dep[x] + dep[y] - 2 * dep[u]);
//		}
//	}
	if (!keep){
		sack.clear();
//		cout << "clear\n";
	}
//	cout << "end calc " << u << '\n' << '\n';
}

int best_path(int N, int K, int H[][2], int L[]) {
	n = N; k = K;
	for (int i = 0; i < n-1; i++){
		adj[H[i][0]].emplace_back(H[i][1], L[i]);
		adj[H[i][1]].emplace_back(H[i][0], L[i]);
	}
	memset(bc, -1, sizeof(bc));
//	for (int i = 0; i < n; i++){
//		cout << i << " : ";
//		for (pii p : adj[i]) cout << '{' << p.fi << ", " << p.se << "} ";
//		cout << '\n';
//	}
	getsz(0);
//	for (int i = 0; i < n; i++){
//		cout << dep[i] << ' ' << dist[i] << ",\n"[i==n-1];
//	}
	dfs(0, -1, 1);
	if (ans == 0x3f3f3f3f) return -1;
	return ans;
}

Compilation message (stderr)

race.cpp: In function 'void getsz(int, int)':
race.cpp:24:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0, nx, w; i < adj[u].size(); i++){
                         ~~^~~~~~~~~~~~~~~
race.cpp: In function 'void dfs(int, int, bool)':
race.cpp:39:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0, nx; i < adj[u].size(); i++){
                      ~~^~~~~~~~~~~~~~~
race.cpp:55:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for (int i = 0, nx, w; i < adj[u].size(); i++){
                         ~~^~~~~~~~~~~~~~~
race.cpp:55:22: warning: unused variable 'w' [-Wunused-variable]
  for (int i = 0, nx, w; i < adj[u].size(); i++){
                      ^

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