Given a string of lowercase letters, print the index of the first character that occurs exactly once in the whole string. If every character repeats, print -1.
Constraints
- 1 ≤ length ≤ 100000
- Only the letters a–z
Input and output
- Input
- One line: the string s
- Output
- One integer: the 0-based index, or -1.
Examples
Input 1
bananaOutput
0b appears once.
Input 2
aabbccOutput
-1Everything repeats.
Show hints
- Count first, then search.
- A 26-slot array is enough for the counts.
Show the explanation
Two passes. First count how many times each letter occurs (26 counters). Then walk the string again and return the first index whose letter has count 1. This is O(n) time and O(1) extra space (26 counters, independent of n).
Original UniCircle question. Last reviewed 21 Oct 2026.