Problem
Return the index of the first character in text that appears exactly once. Case matters.
Implement first_unique_index(text).
Input
text: The text to inspect.
Output
Return the index, or -1 if every character repeats.
Constraints
0 ≤ length ≤ 100,000
Examples
Example 1
Input:
text = "swiss"
Expected output:
expected = 1Input:
std::string text = "swiss";
Expected output:
long long expected = 1;Input:
string text = "swiss";
Expected output:
long expected = 1;Explanation
s repeats, w appears once at index 1.
Example 2
Input:
text = "aabb"
Expected output:
expected = -1Input:
std::string text = "aabb";
Expected output:
long long expected = -1;Input:
string text = "aabb";
Expected output:
long expected = -1;Explanation
Every character repeats: -1.
How to approach it
Try on your own first, then open one hint at a time.
Hint 1
You need characters that appear exactly once, not just the first different one.
Hint 2
Count all character frequencies first, then find the earliest position with frequency one.
Hint 3
Remember that uppercase and lowercase letters are different characters.
Expected complexity
O(n) time, O(k) extra space
References
This challenge is adapted for CodeUtility. Follow the statement and constraints above.