An integer has monotone increasing digits if and only if each pair of adjacent digits x and y satisfy x <= y.
Given an integer n, return the largest number that is less than or equal to n with monotone increasing digits.
Example 1:
Input: n = 10 Output: 9
Example 2:
Input: n = 1234 Output: 1234
Example 3:
Input: n = 332 Output: 299
Constraints:
0 <= n <= 109