first_letter.py

# Given a string s consisting of lowercase English letters, return the first letter
# to appear twice.

# Note:

# A letter a appears twice before another letter b if the second occurrence of a is before
# the second occurrence of b.
# s will contain at least one letter that appears twice.
 

# Example 1:
# Input: s = "abccbaacz"
# Output: "c"
# Explanation:
# The letter 'a' appears on the indexes 0, 5 and 6.
# The letter 'b' appears on the indexes 1 and 4.
# The letter 'c' appears on the indexes 2, 3 and 7.
# The letter 'z' appears on the index 8.
# The letter 'c' is the first letter to appear twice, because out of all the letters the index 
# of its second occurrence is the smallest.

# Example 2:
# Input: s = "abcdd"
# Output: "d"
# Explanation:
# The only letter that appears twice is 'd' so we return 'd'.
 

# Constraints:

# 2 <= s.length <= 100
# s consists of lowercase English letters.
# s has at least one repeated letter.


class Solution:
    def repeatedCharacter(self, s: str) -> str:
        mpp = []

        for i in s:
            if i in mpp:
                return i
            else:
                mpp.append(i)