Submission #786295

#	Time	Username	Problem	Language	Result	Execution time	Memory
786295		vjudge1	Thousands Islands (IOI22_islands)	C++17	39.40 / 100	30 ms	6096 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> f0, f1;
        for (int i = 0; i < M; i++) {
            (U[i] == 0 ? f0 : f1).push_back(i);
        }
        if (f0.size() < 2 || f1.size() < 1) {
            return false;
        }
        return vector{f0[0], f1[0], f0[1], f0[0], f1[0], f0[1]};
    }
    bool S3 = M % 2 == 0;
    bool S4 = M % 2 == 0;
    vector<vector<pair<int, int>>> adj(N);
    for (int i = 0; i < M; i++) {
        if (i % 2 == 1 && (U[i - 1] != V[i] || V[i - 1] != U[i])) {
            S3 = 0;
        }
        if (i % 2 == 1 && (U[i - 1] != U[i] || V[i - 1] != V[i])) {
            S4 = 0;
        }
        adj[U[i]].emplace_back(V[i], i);
    }
    if (S3) {
        int x = 0, y = -1;
        vector<int> p;
        while (1) {
            if (adj[x].size() < 2 - (y == -1)) {
                return false;
            }
            if (adj[x].size() > 2 - (y == -1)) {
                auto ans = p;
                int u, v;
                if (y == -1) {
                    u = adj[x][0].second;
                    v = adj[x][1].second;
                } else {
                    u = adj[x][adj[x][0].second == (y ^ 1) ? 1 : 0].second;
                    v = adj[x][adj[x][2].second == (y ^ 1) ? 1 : 2].second;
                }
                ans.push_back(u);
                ans.push_back(u ^ 1);
                ans.push_back(v);
                ans.push_back(v ^ 1);
                ans.push_back(u ^ 1);
                ans.push_back(u);
                ans.push_back(v ^ 1);
                ans.push_back(v);
                for (int i = p.size() - 1; i >= 0; i--) {
                    ans.push_back(p[i]);
                }
                return ans;
            }
            if (adj[x][0].second == (y ^ 1)) {
                tie(x, y) = adj[x][1];
            } else {
                tie(x, y) = adj[x][0];
            }
            p.push_back(y);
        }
    }
    if (S4) {
        vector<int> vis(N);
        auto dfs = [&](auto dfs, int x) -> bool {
            vis[x] = 1;
            for (auto [y, z] : adj[x]) {
                if (vis[y] == 1) {
                    return 1;
                }
                if (!vis[y]) {
                    if (dfs(dfs, y)) {
                        return 1;
                    }
                }
            }
            vis[x] = 2;
            return 0;
        };
        return dfs(dfs, 0);
    }
    int a, b, c, d;
    for (int i = 0; i < M; i++) {
        if (U[i] == 0) {
            if (V[i] == 1) {
                a = i;
            }
            if (V[i] == 2) {
                c = i;
            }
        }
        if (V[i] == 0) {
            if (U[i] == 1) {
                b = i;
            }
            if (U[i] == 2) {
                d = i;
            }
        }
    }
    return vector{a, b, c, d, b, a, d, c};
}

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:103:41: warning: 'd' may be used uninitialized in this function [-Wmaybe-uninitialized]
  103 |     return vector{a, b, c, d, b, a, d, c};
      |                                         ^
islands.cpp:103:41: warning: 'c' may be used uninitialized in this function [-Wmaybe-uninitialized]
islands.cpp:103:41: warning: 'b' may be used uninitialized in this function [-Wmaybe-uninitialized]
islands.cpp:103:41: warning: 'a' may be used uninitialized in this function [-Wmaybe-uninitialized]

• Subtask 1: 5 / 5
• Subtask 2: 5 / 5
• Subtask 3: 21 / 21
• Subtask 4: 8.399999999999999 / 24
• Subtask 5: 0 / 45