First Non-Repeating Character

Category: Strings

Difficulty: Easy

Description

Write a function that takes in a string of lowercase English-alphabet letters and returns the index of the string's first non-repeating character.

The first non-repeating character is the first character in a string that occurs only once.

If the input string doesn't have any non-repeating characters, your function should return -1.

Sample Input

string = "abcdcaf"

Sample Output

1 // The first non-repeating character is "b" and is found at index 1.

Optimal Space & Time Complexity

O(n) time | O(1) space - where n is the length of the input string\nThe constant space is because the input string only has lowercase\nEnglish-alphabet letters; thus, our hash table will never have more\nthan 26 character frequencies.