https://leetcode.com/problems/find-the-difference/\n\nGiven two strings `s1` and `s2` which are of lengths `n` and `n+1`. The second string contains all the character of the first string, but there is one extra character. Your task to find the extra character in the second string.\n\n**Example:**\n```\nInput: s1 = "abbc", s2 = "bcbad"\nOutput: \'d\'\n```\n\nSimilar problems:\n* https://leetcode.com/problems/single-number

https://leetcode.com/problems/find-the-difference/\n\nGiven two strings s1 and s2 which are of lengths n and n+1. The second string contains all the character o