Given a string consisting of lowercase english alphabets. Find the repeated character present first in the string.
Example 1:
Input:
S = "geeksforgeeks"
Output: g
Explanation: g, e, k and s are the repeating
characters. Out of these, g occurs first.
Example 2:
Input:
S = "abcde"
Output: -1
Explanation: No repeating character present.
Your Task:
You don't need to read input or print anything. Your task is to complete the function firstRep() which takes the string S as input and returns the the first repeating character in the string. In case there's no repeating character present, return '#'.
Expected Time Complexity: O(|S|).
Expected Auxiliary Space: O(1).
Constraints:
1<=|S|<=10^{5}

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