# 161 One Edit Distance

Given two strings S and T, determine if they are both one edit distance apart.

One edit distance means that two strings will be identical by either one update, delete, or add operation.

**The Idea:** This is the type of problem that is fairly simple, but can easily get messy. I've added comments below in the code explains all cases that can happen.

**Complexity:** O(n) time and O(1) space

```python
class Solution(object):
    def isOneEditDistance(self, s, t):
        """
        :type s: str
        :type t: str
        :rtype: bool
        """

        s_larger = len(s) >= len(t)
        t_larger = len(s) <= len(t)
        for i in range(min(len(s), len(t))):
            if s[i] != t[i]:
                # cases:
                # 1. if both are the same length, then both
                # s and t need to be incremented and be the same

                # 2. if s is larger and t is smaller then
                # s can move one iterator to match the length of t
                # and t must remain the same length

                # 3. if t is larger and s is smaller, then
                # the reverse must be true
                return s[i + s_larger:] == t[i + t_larger:]

        # if the lengths are the same return False
        return abs(len(s) - len(t)) == 1


obj = Solution()
print(obj.isOneEditDistance('ab', 'ba'))  # False
print(obj.isOneEditDistance('abc', 'ab'))  # True
print(obj.isOneEditDistance('ab', 'cab'))  # True
print(obj.isOneEditDistance('a', ''))  # True
print(obj.isOneEditDistance('abb', 'abc'))  # True
print(obj.isOneEditDistance('a', 'a'))  # False
print(obj.isOneEditDistance('acc', 'adc'))  # True
print(obj.isOneEditDistance('kkk', 'kkc'))  # True
print(obj.isOneEditDistance('lmk', 'kml'))  # False
print(obj.isOneEditDistance('abcde', 'abfde'))  # True
print(obj.isOneEditDistance('abcde', 'abffe'))  # False
```