String Manipulation String Counting Character
Learner Level

Implement the removeDuplicateCharacters method that returns the text after keeping only the first occurrence of each character.

The input contains a string text. Your task is to remove duplicate characters while keeping the first occurrence of each character.

The original order of the remaining characters must be preserved. For example, banana becomes ban because b, a, and n are kept only the first time they appear.

Example 1
Input:
text (string) = banana
Return:
(string) ban
Example 2
Input:
text (string) = programming
Return:
(string) progamin
Example 3
Input:
text (string) = aaaa
Return:
(string) a

Use a set to remember which characters are already added to the result.

Scan the string from left to right. If a character has not been seen before, append it to the result and mark it as seen. If it is already seen, skip it.

Pseudocode:

function removeDuplicateCharacters(text):
    seen = empty set
    result = empty string
    for each character in text:
        if character not in seen:
            add character to result
            add character to seen
    return result
Run your code to see the result.