389 Find the Difference

Given two strings s and t which consist of only lowercase letters.

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

Find the letter that was added in t.

Example:

Input:
s = "abcd"
t = "abcde"

Output:
e

Explanation: 'e' is the letter that was added.

The Idea: Sort the strings and return the first non matching character. Otherwise return the last character of t.

Complexity: O(2nlog(n) + n) time and O(2n) space

def findTheDifference(self, s, t):
    """
    :type s: str
    :type t: str
    :rtype: str
    """

    s_list = sorted(s)
    t_list = sorted(t)

    for s_char, t_char in zip(s_list, t_list):
        if s_char is not t_char:
            return t_char

    return t_list[-1]