<p>Given two integers n and k, return <em>an array of all the integers of length </em><code>n</code><em> where the difference between every two consecutive digits is </em><code>k</code>. You may return the answer in <strong>any order</strong>.</p>

<p>Note that the integers should not have leading zeros. Integers as <code>02</code> and <code>043</code> are not allowed.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> n = 3, k = 7
<strong>Output:</strong> [181,292,707,818,929]
<strong>Explanation:</strong> Note that 070 is not a valid number, because it has leading zeroes.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> n = 2, k = 1
<strong>Output:</strong> [10,12,21,23,32,34,43,45,54,56,65,67,76,78,87,89,98]
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>2 &lt;= n &lt;= 9</code></li>
	<li><code>0 &lt;= k &lt;= 9</code></li>
</ul>

class Solution {
 public:
  vector<int> numsSameConsecDiff(int n, int k) {
    if (n == 1)
      return {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};

    vector<int> ans;

    if (k == 0) {
      for (char c = '1'; c <= '9'; ++c)
        ans.push_back(stoi(string(n, c)));
      return ans;
    }

    for (int num = 1; num <= 9; ++num)
      dfs(n - 1, k, num, ans);

    return ans;
  }

 private:
  void dfs(int n, int k, int num, vector<int>& ans) {
    if (n == 0) {
      ans.push_back(num);
      return;
    }

    const int lastDigit = num % 10;

    for (const int nextDigit : {lastDigit - k, lastDigit + k})
      if (0 <= nextDigit && nextDigit <= 9)
        dfs(n - 1, k, num * 10 + nextDigit, ans);
  }
};
10800