Submission #767208

#	Time	Username	Problem	Language	Result	Execution time	Memory
767208		t6twotwo	Thousands Islands (IOI22_islands)	C++17	6.75 / 100	26 ms	4556 KiB

islands

#include "islands.h"
#include <bits/stdc++.h>
using namespace std;
variant<bool, vector<int>> find_journey(int N, int M, vector<int> U, vector<int> V) {
    if (N == 2) {
        vector<int> a, b;
        for (int i = 0; i < M; i++) {
            if (U[i] == 0) {
                a.push_back(i);
            } else {
                b.push_back(i);
            }
        }
        if (a.size() >= 2 && b.size() >= 1) {
            return vector{a[0], b[0], a[1], a[0], b[0], a[1]};
        } else {
            return false;
        }
    }
    bool subtask3 = 0;
    bool subtask4 = 0;
    if (M % 2 == 0) {
        subtask3 = 1;
        subtask4 = 0;
        for (int i = 0; i < M; i += 2) {
            if (U[i] != V[i + 1] || V[i] != U[i + 1]) {
                subtask3 = 0;
            }
            if (U[i] != U[i + 1] || V[i] != V[i + 1]) {
                subtask4 = 0;
            }
        }
    }
    if (subtask3) {
        vector<vector<pair<int, int>>> adj(N);
        for (int i = 0; i < M; i++) {
            adj[U[i]].emplace_back(V[i], i);
        }
        vector<bool> vis(N);
        int x = 0, p = -1;
        while (1) {
            vis[x] = 1;
            if ((x == 0 && adj[x].size() > 1) || (x != 0 && adj[x].size() > 2)) {
                return true;
            }
            if ((x == 0 && adj[x].empty()) || (x != 0 && adj[x].size() == 1)) {
                return false;
            }
            if (x == 0) {
                x = adj[x][0].first;
                continue;
            }
            int t = p; p = x;
            x = adj[x][0].first ^ adj[x][1].first ^ t;
            if (vis[x]) {
                return true;
            }
        }
        return false;
    }
    int s[3][3];
    for (int i = 0; i < M; i++) {
        if (U[i] < 3 && V[i] < 3) {
            s[U[i]][V[i]] = i;
        }
    }
    return vector{s[0][1], s[1][2], s[2][0], s[0][2], s[2][1], s[1][0], s[2][0], s[1][2], s[0][1], s[1][0], s[2][1], s[0][2]};
}

Compilation message (stderr)

islands.cpp: In function 'std::variant<bool, std::vector<int, std::allocator<int> > > find_journey(int, int, std::vector<int>, std::vector<int>)':
islands.cpp:21:10: warning: variable 'subtask4' set but not used [-Wunused-but-set-variable]
   21 |     bool subtask4 = 0;
      |          ^~~~~~~~

• Subtask 1: 5 / 5
• Subtask 2: 1.75 / 5
• Subtask 3: 0 / 21
• Subtask 4: 0 / 24
• Subtask 5: 0 / 45