How should I practice First Non-Repeating Character?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Goldman Sachs phone screen and onsite interview problems in FastPrep.

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First Non-Repeating Character

Goldman Sachs● EasyFULLTIMENEW GRADPHONE SCREENONSITE INTERVIEW

Problem statement

Given a non-empty string text containing lowercase English letters, return its first character that occurs exactly once.

The first character is determined by its position in text, not by alphabetical order. If every character repeats, return the empty string "".

Function

firstNonRepeatingCharacter(text: String) → String

Examples

Example 1

text = "swiss"return = "w"

The letter s repeats. The next character, w, occurs once, so it is the first non-repeating character.

Example 2

text = "aabbc"return = "c"

Both a and b occur twice, while c occurs once.

Example 3

text = "aabb"return = ""

No character occurs exactly once, so the result is the empty string.

Constraints

1 <= text.length <= 10^5
text contains only lowercase English letters.