#1370

Increasing Decreasing String

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Description

You are given a string s. Reorder the string using the following algorithm:

- Remove the smallest character from s and append it to the result.

- Remove the smallest character from s that is greater than the last appended character, and append it to the result.

- Repeat step 2 until no more characters can be removed.

- Remove the largest character from s and append it to the result.

- Remove the largest character from s that is smaller than the last appended character, and append it to the result.

- Repeat step 5 until no more characters can be removed.

- Repeat steps 1 through 6 until all characters from s have been removed.

If the smallest or largest character appears more than once, you may choose any occurrence to append to the result.

Return the resulting string after reordering s using this algorithm.

Example 1:

Input: s = "aaaabbbbcccc"

Output: "abccbaabccba"

Explanation: After steps 1, 2 and 3 of the first iteration, result = "abc"

After steps 4, 5 and 6 of the first iteration, result = "abccba"

First iteration is done. Now s = "aabbcc" and we go back to step 1

After steps 1, 2 and 3 of the second iteration, result = "abccbaabc"

After steps 4, 5 and 6 of the second iteration, result = "abccbaabccba"

Example 2:

Input: s = "rat"

Output: "art"

Explanation: The word "rat" becomes "art" after re-ordering it with the mentioned algorithm.

Solution