Submission #328846

#	Time	Username	Problem	Language	Result	Execution time	Memory
328846		dolphingarlic	Stations (IOI20_stations)	C++14	100 / 100	995 ms	1144 KiB

stations

/*
IOI 2020 Stations
- Just alternate between tin and tout
- Complexity: O(N) with max_label == N - 1
*/

#include "stations.h"
#include <vector>
#include <algorithm>

std::vector<int> graph[1000];
int tin[1000], tout[1000], timer;

void dfs(int node = 0, int parent = -1) {
    tin[node] = timer++;
    for (int i : graph[node]) if (i != parent) dfs(i, node);
    tout[node] = timer++;
}

std::vector<int> label(int n, int k, std::vector<int> u, std::vector<int> v) {
    for (int i = 0; i < n; i++) graph[i].clear();
    for (int i = 0; i < n - 1; i++) {
        graph[u[i]].push_back(v[i]);
        graph[v[i]].push_back(u[i]);
    }
    timer = 0;
    dfs();
    std::vector<int> labels(n);
    for (int i = 0; i < n; i++) {
        labels[i] = tin[i] * (tin[i] - 1 & 1) + tout[i] * (tout[i] - 1 & 1) >> 1;
    }
    return labels;
}

int find_next_station(int s, int t, std::vector<int> c) {
    if (s < c.back()) {
        if (t < s || t > c.back()) return c.back();
        return *std::lower_bound(c.begin(), c.end(), t);
    } else {
        if (t > s || t < c[0]) return c[0];
        return *prev(std::upper_bound(c.begin(), c.end(), t));
    }
}

Compilation message (stderr)

stations.cpp: In function 'std::vector<int> label(int, int, std::vector<int>, std::vector<int>)':
stations.cpp:30:38: warning: suggest parentheses around '-' in operand of '&' [-Wparentheses]
   30 |         labels[i] = tin[i] * (tin[i] - 1 & 1) + tout[i] * (tout[i] - 1 & 1) >> 1;
      |                               ~~~~~~~^~~
stations.cpp:30:68: warning: suggest parentheses around '-' in operand of '&' [-Wparentheses]
   30 |         labels[i] = tin[i] * (tin[i] - 1 & 1) + tout[i] * (tout[i] - 1 & 1) >> 1;
      |                                                            ~~~~~~~~^~~
stations.cpp:30:47: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
   30 |         labels[i] = tin[i] * (tin[i] - 1 & 1) + tout[i] * (tout[i] - 1 & 1) >> 1;
      |                     ~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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