311. First Unique Character in a String
Easy
Frequency Map
Hashing
Problem
Given a string s, find the first character that appears exactly once and return its index. Return -1 if no unique character exists.
Examples
Example 1
Input: "leetcode"
Output: 0
Example 2
Input: "loveleetcode"
Output: 2
Example 3
Input: "aabb"
Output: -1
Constraints
� 1 <= s.length <= 100000
� s consists of lowercase English letters.
Hints
?? Count every character first.
?? Scan the original string again and return the first position whose frequency is one.
Expected Complexity
Time: O(n)
Space: O(1)
Follow-up
How would you solve this for a stream of characters where the first unique character must be queried repeatedly?
Practice Notes
Attempts: 0
Time spent: 0min
Hints used: 0
JavaScript
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Case 1
Case 2
Case 3
Input
"leetcode"Expected
0