Given an array of positive integers arr, return the lexicographically largest permutation that is smaller than arr and can be formed by swapping two elements at distinct indices exactly once. If no such permutation exists, return arr unchanged.

Constraints:

• $1 \leq$ arr.length $\leq 10^4$

• $1 \leq$ arr[i] $\leq 10^4$

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We have a game for you to play. Rearrange the logical building blocks to develop a clearer understanding of how to solve this problem.

Implement your solution in the following coding playground.