dsa · easy
First Unique Character in a String
You are given a string s of lowercase letters. Return the index of the first character that appears exactly once in the whole string. If no such character exists, return -1.
Arguments
s— the input string
Example
s = "loveleetcode"
Counting each letter, l appears twice, o twice, v once — but v is at index 2 and nothing before it appears once, so the answer is 2.
s = "aabb" → every letter repeats → -1.
Constraints
1 <= s.length <= 10^5 s consists of lowercase letters Hidden tests include near-max size for this bound; a slower-than-intended solution TLEs.
Examples
Example 1
Input: "loveleetcode" Expected: 2
Example 2
Input: "aabb" Expected: -1
Example 3
Input: "z" Expected: 0