# 1370. Increasing Decreasing String

<https://leetcode.com/problems/increasing-decreasing-string>

## Description

Given a string `s`. You should re-order the string using the following algorithm:

1. Pick the **smallest** character from `s` and **append** it to the result.
2. Pick the **smallest** character from `s` which is greater than the last appended character to the result and **append** it.
3. Repeat step 2 until you cannot pick more characters.
4. Pick the **largest** character from `s` and **append** it to the result.
5. Pick the **largest** character from `s` which is smaller than the last appended character to the result and **append** it.
6. Repeat step 5 until you cannot pick more characters.
7. Repeat the steps from 1 to 6 until you pick all characters from `s`.

In each step, If the smallest or the largest character appears more than once you can choose any occurrence and append it to the result.

Return *the result string* after sorting `s` with 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.
```

**Example 3:**

```
**Input:** s = "leetcode"
**Output:** "cdelotee"
```

**Example 4:**

```
**Input:** s = "ggggggg"
**Output:** "ggggggg"
```

**Example 5:**

```
**Input:** s = "spo"
**Output:** "ops"
```

**Constraints:**

* `1 <= s.length <= 500`
* `s` contains only lower-case English letters.

## ac

```java
```


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://jaywin.gitbook.io/leetcode/solutions/1370-increasing-decreasing-string.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.