SDE - 2

This question is very similar to the basic "Rotten Oranges: question. 
I applied BFS to resolve this question.

Tip 1: Try to first understand what the question means. 
Tip 2: Think of ways not brute force but something out of the box that might help you achieve this task. 
 

This is a medium-type question. First I was confused about the understanding of the question. Then after trying out the few questions and examples as stated by interviewers, I understood I needed to do some reshuffling of the number such that among all the greater numbers I got I needed to get the smallest among them. 

Then after trying out a few examples, I found that If I try to put the largest number on the leftmost side it will give me a greater number but I cannot guarantee it is the next greatest only. So it was clear I only needed to change from the rightmost position. Then I started experimenting with the rightmost digit and thought about where should I place it so I get a greater number. The answer was easy from here, if I replace it with the closest smaller digit I will get the next greater number. 
Finally, by doing such kind of deductions, I concluded and started drafting the solution. 

I did not clear this round because my code did not pass all the test cases. It missed on corner condition. 
There is an extra sorting step that we also need to perform once we do the switching of the letters.