2024 AMC 10A Problem 6
What is the minimum number of successive swaps of adjacent letters in the string that are needed to change the string to ? (For example, swaps are required to change to ; one such sequence of swaps is .)
In we can move to the first position by swaps.
So, .
If you want to prove it rigorously that the answer is not less than you can assign to to to respectively and use the number of inversions
By each swap the number of inversions changes by .
So we need at least swaps to go to from .
Therefore .
By Hint 3, .
So we need at least swaps to go to from .
Therefore .
By Hint 3, .
(D) 15