I'm posting my code for a LeetCode problem copied here. If you have time and would like to review, please do so. Thank you!


  • There is a box protected by a password. The password is a sequence of n digits where each digit can be one of the first k digits 0, 1, ..., k-1.

  • While entering a password, the last n digits entered will automatically be matched against the correct password.

  • For example, assuming the correct password is "345", if you type "012345", the box will open because the correct password matches the suffix of the entered password.

  • Return any password of minimum length that is guaranteed to open the box at some point of entering it.

Accepted Code

#include <vector>
#include <string>

class Solution {
    int n;
    int k;
    int value;
    std::vector<std::vector<bool>> visited;
    std::string base_sequence;

    std::string crackSafe(int n, int k) {
        if (k == 1) {
            return std::string(n, '0');

        this->n = n;
        this->k = k;
        value = 1;

        for (int index = 0; index < n - 1; index++) {
            value *= k;

        visited.resize(value, std::vector<bool>(k, false));
        return base_sequence + base_sequence.substr(0, n - 1);

    // Depth first search the neighbor value
    void depth_first_search(int neighbor) {
        for (int index = 0; index < k; index++) {
            if (!visited[neighbor][index]) {
                visited[neighbor][index] = true;
                depth_first_search((neighbor * k + index) % value);
                base_sequence.push_back('0' + index);


LeetCode has a template for answering questions. There is usually a class named Solution with one or more public functions which we are not allowed to rename.


1 Answer 1


Constant members

n and k can be constant, so long as

  • you remove them from being parameters to crackSafe
  • you add them as parameters to a constructor
  • the constructor uses inline initialization syntax, i.e. n(n)

Basically, your two member functions should - in their current form - be bare functions outside of a class, since the class member variables only really have transient meaning. For this to make sense as a class, n and k would only make sense as "permanent" attributes per instance.


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