Submission #767255

#	Time	Username	Problem	Language	Result	Execution time	Memory
767255		t6twotwo	Thousands Islands (IOI22_islands)	C++17	17.35 / 100	64 ms	11780 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 = 1;
        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<map<int, int>> T(N);
        vector<vector<int>> adj(N);
        for (int i = 0; i < M; i++) {
            adj[U[i]].push_back(V[i]);
            T[U[i]][V[i]] = i;
        }
        vector<int> ans;
        int x = 0, p = -1;
        while (1) {
            vector<int> f;
            for (int y : adj[x]) {
                if (y != p) {
                    f.push_back(y);
                }
            }
            if (f.empty()) {
                return false;
            }
            if (f.size() == 1) {
                ans.push_back(T[x][f[0]]);
                p = x;
                x = f[0];
                continue;
            }
            auto v = ans;
            vector<int> s(M);
            ans.push_back(T[x][f[0]]);
            ans.push_back(T[f[0]][x]);
            int z = 0;
            for (int y : ans) {
                if (s[y] == 0) {
                    assert(z == U[y]);
                    z = V[y];
                    s[y] = 1;
                } else {
                    assert(z == V[y]);
                    z = U[y];
                    s[y] = 0;
                }
            }
            assert(z == x);
            assert(T[x].count(f[1]));
            ans.push_back(T[x][f[1]]);
            ans.push_back(T[f[1]][x]);
            // assert(x == z);
            ans.push_back(T[f[0]][x]);
            ans.push_back(T[x][f[0]]);
            ans.push_back(T[f[1]][x]);
            ans.push_back(T[x][f[1]]);
            for (int i = v.size() - 1; i >= 0; i--) {
                ans.push_back(v[i]);
            }
            // vector<int> s(M);
            // x = 0;
            // for (int y : ans) {
            //     if (s[y] == 0) {
            //         assert(x == U[y]);
            //         x = V[y];
            //         s[y] = 1;
            //     } else {
            //         assert(x == V[y]);
            //         x = U[y];
            //         s[y] = 0;
            //     }
            // }
            // assert(x == 0);
            // assert(s == vector<int>(M));
            return ans;
        }
    }
    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: 5 / 5
• Subtask 3: 7.35 / 21
• Subtask 4: 0 / 24
• Subtask 5: 0 / 45