Find First Repeated Character in a String

Given a string 'STR' composed of lowercase English letters, identify the character that repeats first in terms of its initial occurrence.

Example:

Input:

STR = "abccba"

Output:

"a"

Explanation:

Although the first repeating character is 'c', the character 'a' is the first repeated character by initial appearance.

Constraints:

• 1 <= T <= 200
• 0 <= length of S <= 10000
• ‘S’ consists of lowercase English alphabets.

In the scenario where no repeated character exists, output '%'.

Note:

Ensure that you return the repeated character that appears first, rather than simply the first character that repeats. If there are no repeating characters, return '%'. The function to implement is called “repeatedCharacter”.