Find the Difference

You are given two strings s and t.

String t is generated by random shuffling string s and then add one more letter at a random position.

Return the letter that was added to t.

Example 1:

Input: s = "abcd", t = "abcde"
Output: "e"
Explanation: 'e' is the letter that was added.

Example 2:

Input: s = "", t = "y"
Output: "y"

Constraints:

• 0 <= s.length <= 1000
• t.length == s.length + 1
• s and t consist of lowercase English letters.

SOLUTION:

class Solution:
    def findTheDifference(self, s: str, t: str) -> str:
        ctr = {}
        for c in t:
            ctr[c] = ctr.get(c, 0) + 1
        for c in s:
            ctr[c] -= 1
            if ctr[c] == 0:
                del ctr[c]
        return list(ctr)[0]