389. Find the Difference-找不同

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"

Example 3:
Input: s = "a", t = "aa"
Output: "a"

Example 4:
Input: s = "ae", t = "aea"
Output: "a"

Constraints:

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

Solution in python:

class Solution:
    def findTheDifference(self, s: str, t: str) -> str:
        if len(s) == 0:
            return t 
        adic = {}
        for item in s:
            if item not in adic.keys():
                adic[item] = 1
            else:
                adic[item] += 1
        for item in t:
            if item not in adic.keys():
                return item
            else:
                adic[item] -= 1
                if adic[item] < 0:
                    return item