Submission #622593

#	Time	Username	Problem	Language	Result	Execution time	Memory
622593		erekle	Stations (IOI20_stations)	C++17	100 / 100	972 ms	744 KiB

stations

#include "stations.h"
#include <bits/stdc++.h>

using namespace std;

vector<vector<int>> g;
vector<int> tin, tout, depth;
int t;
void dfs(int node, int parent = -1) {
	if (parent == -1) depth[node] = 0;
	else depth[node] = depth[parent] + 1;

	tin[node] = ++t;
	for (int child : g[node]) {
		if (child != parent) dfs(child, node);
	}
	tout[node] = ++t;
}

void compress(vector<int> &v) {
	vector<int> u = v;
	sort(u.begin(), u.end());
	// all values already unique
	for (int &x : v) {
		x = lower_bound(u.begin(), u.end(), x) - u.begin();
	}
}

vector<int> label(int n, int k, vector<int> u, vector<int> v) {
	g.clear(), tin.clear(), tout.clear(), depth.clear();
	g.resize(n);
	for (int i = 0; i < u.size(); ++i) {
		g[u[i]].push_back(v[i]);
		g[v[i]].push_back(u[i]);
	}
	t = -1;
	tin.resize(n), tout.resize(n);
	depth.resize(n);
	dfs(0);

	vector<int> labels(n);
	for (int i = 0; i < n; i++) {
		if (depth[i] & 1) labels[i] = tout[i];
		else labels[i] = tin[i];
	}
	compress(labels);
	return labels;
}

int find_next_station(int s, int t, vector<int> c) {
	int m = c.size();
	if (m == 1) return c[0];
	sort(c.begin(), c.end());
	if (s < c.front()) { // s has tin, rest have tout
		// c.back() is parent of s
		if (s <= t && t <= c[m-2]) {
			// t is in subtree of s
			// which child
			for (int x : c) {
				if (t <= x) return x;
			}
		} else {
			// t is not in subtree of s
			return c.back();
		}
	} else { // s has tout, rest have tin
		// c.front() is parent of s
		if (c[1] <= t && t <= s) {
			// t is in subtree of s
			// which child
			for (int i = m-1; i >= 0; --i) {
				if (t >= c[i]) return c[i];
			}
		} else {
			// t is not in subtree of s
			return c.front();
		}
	}
}

Compilation message (stderr)

stations.cpp: In function 'std::vector<int> label(int, int, std::vector<int>, std::vector<int>)':
stations.cpp:32:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   32 |  for (int i = 0; i < u.size(); ++i) {
      |                  ~~^~~~~~~~~~
stations.cpp: In function 'int find_next_station(int, int, std::vector<int>)':
stations.cpp:79:1: warning: control reaches end of non-void function [-Wreturn-type]
   79 | }
      | ^

• Subtask 1: 5 / 5
• Subtask 2: 8 / 8
• Subtask 3: 16 / 16
• Subtask 4: 10 / 10
• Subtask 5: 61 / 61