Given a string, find the first character that doesn't repeat.
Input: A single string.
Output: The first non-repeating character, or "None" if all characters repeat.
Examples:
- Input:
"leetcode"-> Output:"l"(appears only once, and is first) - Input:
"aabbcc"-> Output:"None"(all characters repeat)
This requires counting occurrences, then finding the first with count .