All problems
First Non-Repeating Character
Problem
Return the index of the first character in a string that does not repeat anywhere else.
Count how often each character occurs, then scan left to right for the first character whose count is one. Return -1 if no such character exists, including for the empty string.
Hint
Build a frequency map first, then scan the string again.
Test cases
case 1
in: ["leetcode"]
expected: 0
case 2
in: ["loveleetcode"]
expected: 2
case 3
in: ["aabb"]
expected: -1
case 4
in: [""]
expected: -1
case 5
in: ["z"]
expected: 0
Starter codePython
def first_unique_char(s):
# Your code here
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