[Google Onsite] String Conversion

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(This question has been seen in the interviews of the following companies: Google)

Given 2 strings s and t, determine if you can convert s into t. The rules are:

You can change 1 letter at a time.
Once you changed a letter you have to change all occurrences of that letter. Example 1:

Input: s = "abca", t = "dced"
Output: true
Explanation: abca ('a' to 'd') -> dbcd ('c' to 'e') -> dbed ('b' to 'c') -> dced
Example 2:

Input: s = "ab", t = "ba"
Output: true
Explanation: ab -> ac -> bc -> ba
Example 3:

Input: s = "abcdefghijklmnopqrstuvwxyz", t = "bcdefghijklmnopqrstuvwxyza"
Output: false
Example 4:

Input: s = "aa", t = "cd"
Output: false
Example 5:

Input: s = "ab", t = "aa"
Output: true
Example 6:

Input: s = "abcdefghijklmnopqrstuvwxyz", t = "bbcdefghijklmnopqrstuvwxyz"
Output: true
Both strings contain only lowercase English letters.

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