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Count characters

Here’s your count_characters.md file properly formatted in Markdown with clear structure and consistent code formatting:

# Count Characters, Remove Duplicates, and Sort

## Problem (LeetCode Style)
Given a string `s`, count the occurrence of each character, remove duplicate characters, and return a string of unique characters sorted in ascending order based on their ASCII value.

### Constraints
- `1 <= s.length <= 10^5`
- `s` contains printable ASCII characters.

### Examples
```text
Input: "banana"
Output: "abn"

Input: "programming"
Output: "agimnopr"

Approach

  1. Count each character manually.
  2. Track characters to avoid duplicates.
  3. Sort manually without using built-in sort.

TypeScript Code

function countAndSortUnique(s: string): string {
    let count: { [key: string]: number } = {};
    let uniqueChars: string[] = [];

    // Count characters and track unique ones
    for (let i = 0; i < s.length; i++) {
        const c = s[i];
        if (!count[c]) {
            count[c] = 1;
            uniqueChars.push(c);
        } else {
            count[c]++;
        }
    }

    // Manual sort of unique characters (ascending ASCII order)
    for (let i = 0; i < uniqueChars.length - 1; i++) {
        for (let j = i + 1; j < uniqueChars.length; j++) {
            if (uniqueChars[i] > uniqueChars[j]) {
                const temp = uniqueChars[i];
                uniqueChars[i] = uniqueChars[j];
                uniqueChars[j] = temp;
            }
        }
    }

    return uniqueChars.join('');
}

This version uses:  
- Proper Markdown headings and subheadings.  
- Consistent code block formatting.  
- Inline comments in TypeScript for clarity.  
- Clear separation of examples and approach.  

If you want, I can also make the **sorting approach more efficient** for large strings while keeping it manual, since the current nested loop is `O(n²)`. Do you want me to do that?