prob05

$\huge\color{cadetblue}{\text{Next smaller number}}$

Given is a positive integer $n \leq 10^{18}$. You are asked to find the largest integer $m$ such that $m < n$ and $m$ has the same digits as $n$. If there is no such $m$, then the output should be $-1$. Also return $-1$ if the next smaller number with the same digits has a leading zero. You are not allowed to use a sorting algorithm.

$\Large\color{darkseagreen}{\text{Examples}}$

Input: 632
Output: 623

Input: 123656789
Output: 123598766

Input: 100
Output: -1