One Edit Distance

Given two strings s and t, return true if they are both exactly one edit distance apart, otherwise return false. A string s is said to be one edit distance apart from a string t if you can transform s into t by performing exactly one of the following operations:

• Insert exactly one character into s to get t.
• Delete exactly one character from s to get t.
• Replace exactly one character of s with a different character to get t. Equal strings are not one edit distance apart — the count of edits must be exactly one.