Chess board tour

#include <bits/stdc++.h>

using namespace std;

bool dfs(int x, int y, int seen, vector<vector<bool>> &visited, int n, int m, vector<char> &output) {

    if (visited[x][y]) {
        if (x == 0 && y == 0) {
            if (seen < n * m) return false;
            return true;
        }
        return false;
    }

    bool touch_up = (y == 0);
    bool touch_left = (x == 0);
    bool touch_right = (x == n-1);
    bool touch_down = (y == m-1);

    bool can_go_left = (x > 0 && !visited[x-1][y]);
    bool can_go_right = (x+1 < n && !visited[x+1][y]);
    bool can_go_up = (y > 0 && !visited[x][y-1]);
    bool can_go_down = (y+1 < m && !visited[x][y+1]);

    if (touch_up && (can_go_left && can_go_right)) return false;
    if (touch_down && (can_go_left && can_go_right)) return false;
    if (touch_left && (can_go_up && can_go_down)) return false;
    if (touch_right && (can_go_up && can_go_down)) return false;

    visited[x][y] = true;

    if (x > 0 && (!visited[x-1][y] || (x-1 == 0 && y == 0))) {
        output.push_back('U');
        bool b = dfs(x-1, y, seen+1, visited, n, m, output);
        if (b) return true;
        output.pop_back();
    }

    if (x+1 < n && !visited[x+1][y]) {
        output.push_back('D');
        bool b = dfs(x+1, y, seen+1, visited, n, m, output);
        if (b) return true;
        output.pop_back();
    }

    if (y > 0 && (!visited[x][y-1] || (x == 0 && y-1 == 0))) {
        output.push_back('L');
        bool b = dfs(x, y-1, seen+1, visited, n, m, output);
        if (b) return true;
        output.pop_back();
    }

    if (y+1 < m && !visited[x][y+1]) {
        output.push_back('R');
        bool b = dfs(x, y+1, seen+1, visited, n, m, output);
        if (b) return true;
        output.pop_back();
    }

    visited[x][y] = false;

    return false;

}

/*
void dfs(int x, int y, int n, int m) {

    vector<vector<bool>> visited(n, vector<bool>(m, false));

    typedef struct {
        int x, y, seen;
    } state_t;

    stack<state_t> s;
    s.push({ x, y, 0 });

    vector<char> events;

    while (!s.empty()) {

        state_t pos = s.top();
        s.pop();

        if (visited[pos.x][pos.y]) {
            if (pos.x == 0 && pos.y == 0) {
                //
                if (pos.seen < n * m)
                    continue;
                else {
                    bool found = false;
                    for (int i = 0; i < n; i++) {
                        for (int j = 0; j < m; j++) {
                            if (!visited[i][j]) {
                                found = true;
                                break;
                            }
                        }
                        if (found) break;
                    }
                    if (found) continue;

                    cout << "ok" << endl;
                }
            }
            continue;
        }
        
        visited[pos.x][pos.y] = true;

        if (pos.x > 0 && !visited[pos.x-1][pos.y]) {
            events.push_back('L');
            s.push({ pos.x-1, pos.y, pos.seen+1 });

        }

        if (pos.x+1 < n && !visited[pos.x+1][pos.y]) {
            events.push_back('D');
            s.push({ pos.x+1, pos.y, pos.seen+1 });
        }

        if (pos.y > 0 && !visited[pos.x][pos.y-1]) {
            events.push_back('U');
            s.push({ pos.x, pos.y-1, pos.seen+1 });
        }

        if (pos.y+1 < m && !visited[pos.x][pos.y+1]) {
            events.push_back('D');
            s.push({ pos.x, pos.y+1, pos.seen+1 });
        }
        
    }

}
*/

int main() {

    int n, m;
    cin >> n >> m;

    vector<vector<bool>> visited(n, vector<bool>(m, false));
    vector<char> output;
    bool b = dfs(0, 0, 0, visited, n, m, output);

    if (!b) {
        cout << -1 << endl;
    } else {
        for (char c : output)
            cout << c;
        cout << endl;
    }

}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED

Test 17

Verdict: ACCEPTED

Test 18

Verdict: ACCEPTED

Test 19

Verdict: ACCEPTED

Test 20

Verdict: ACCEPTED

Test 21

Verdict: TIME LIMIT EXCEEDED

Test 22

Verdict: ACCEPTED

Test 23

Verdict: TIME LIMIT EXCEEDED

Test 24

Verdict: ACCEPTED

Test 25

Verdict: ACCEPTED

Test 26

Verdict: ACCEPTED

Test 27

Verdict: TIME LIMIT EXCEEDED

Test 28

Verdict: TIME LIMIT EXCEEDED

Test 29

Verdict: TIME LIMIT EXCEEDED

Test 30

Verdict: TIME LIMIT EXCEEDED

Test 31

Verdict: TIME LIMIT EXCEEDED

Test 32

Verdict: TIME LIMIT EXCEEDED

Test 33

Verdict: TIME LIMIT EXCEEDED

Test 34

Verdict: TIME LIMIT EXCEEDED

Test 35

Verdict: TIME LIMIT EXCEEDED

Test 36

Verdict: TIME LIMIT EXCEEDED

Test 37

Verdict: TIME LIMIT EXCEEDED

Test 38

Verdict: TIME LIMIT EXCEEDED

Test 39

Verdict: TIME LIMIT EXCEEDED

Test 40

Verdict: TIME LIMIT EXCEEDED

Test 41

Verdict: TIME LIMIT EXCEEDED

Test 42

Verdict: TIME LIMIT EXCEEDED

Test 43

Verdict: TIME LIMIT EXCEEDED

Test 44

Verdict: TIME LIMIT EXCEEDED

Test 45

Verdict: TIME LIMIT EXCEEDED

Test 46

Verdict: TIME LIMIT EXCEEDED

Test 47

Verdict: TIME LIMIT EXCEEDED

Test 48

Verdict: TIME LIMIT EXCEEDED

Test 49

Verdict: TIME LIMIT EXCEEDED

Test 50

Verdict: TIME LIMIT EXCEEDED

Test 51

Verdict: TIME LIMIT EXCEEDED

Test 52

Verdict: TIME LIMIT EXCEEDED

Test 53

Verdict: TIME LIMIT EXCEEDED

Test 54

Verdict: TIME LIMIT EXCEEDED

Test 55

Verdict: TIME LIMIT EXCEEDED

Test 56

Verdict: TIME LIMIT EXCEEDED