75. Remove Duplicate Characters from a String

You are given a null-terminated string containing lowercase and uppercase letters, digits, symbols, or spaces.

Your task is to:

• Remove all duplicate characters from the string
• Keep only the first occurrence of each character

The order of characters must be preserved.
 

Example-1

Input: "programming"
Output: progamin

Example-2

Input: "aabbcc"
Output: abc

Example-3

Input: "C language"
Output: C langue