First Unique Character

Problema

Return the index of the first character in text that appears exactly once. Case matters.

Implement first_unique_index(text).

text: The text to inspect.

Return the index, or -1 if every character repeats.

0 ≤ length ≤ 100,000

Ejemplo 1

Entrada:
text = "swiss"

Salida esperada:
expected = 1

Entrada:
std::string text = "swiss";

Salida esperada:
long long expected = 1;

Entrada:
string text = "swiss";

Salida esperada:
long expected = 1;

s repeats, w appears once at index 1.

Ejemplo 2

Entrada:
text = "aabb"

Salida esperada:
expected = -1

Entrada:
std::string text = "aabb";

Salida esperada:
long long expected = -1;

Entrada:
string text = "aabb";

Salida esperada:
long expected = -1;

Every character repeats: -1.

Inténtalo primero por tu cuenta y luego abre las pistas una a una.

Pista 1

You need characters that appear exactly once, not just the first different one.

Pista 2

Count all character frequencies first, then find the earliest position with frequency one.

Pista 3

Remember that uppercase and lowercase letters are different characters.

Complejidad esperada

O(n) time, O(k) extra space

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