'''
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.
'''

class Solution(object):
    def findTheDifference(self, s, t):
        """
        :type s: str
        :type t: str
        :rtype: str
        """
        frequency = {}
        for c in s:
            if c not in frequency:
                frequency[c] = 1
            else:
                frequency[c] += 1
                
        for c in t:
            if c not in frequency:
                return c
            frequency[c] -= 1
            if frequency[c] < 0:
                return c
            
        return ''

'''
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.
'''

class Solution(object):
    def findTheDifference(self, s, t):
        """
        :type s: str
        :type t: str
        :rtype: str
        """
        frequency = {}
        for c in s:
            if c not in frequency:
                frequency[c] = 1
            else:
                frequency[c] += 1
                
        for c in t:
            if c not in frequency:
                return c
            frequency[c] -= 1
            if frequency[c] < 0:
                return c
            
        return ''

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. :type s: str         :type t: str         :rtype: str