# Question

Given two strings s and t, determine if they are both one edit distance apart.

Note:

There are 3 possiblities to satisify one edit distance apart:

- Insert a character into s to get t
- Delete a character from s to get t
- Replace a character of s to get t

Example 1:

```
Input: s = "ab", t = "acb"
Output: true
Explanation: We can insert 'c' into s to get t.
```

Example 2:

```
Input: s = "cab", t = "ad"
Output: false
Explanation: We cannot get t from s by only one step.
```

Example 3:

```
Input: s = "1203", t = "1213"
Output: true
Explanation: We can replace '0' with '1' to get t.
```

# Solution

```
class Solution(object):
def isOneEditDistance(self, s, t):
"""
:type s: str
:type t: str
:rtype: bool
"""
if len(s) == len(t):
if s == t:
return False
left = 0
while s[left] == t[left] and left < len(s):
left += 1
right = len(s) - 1
while s[right] == t[right] and right >= 0:
right -= 1
return left == right
elif not -1 <= len(s) - len(t) <= 1:
return False
else:
if len(t) > len(s):
s, t = t, s
# s is longer than t by 1
left = 0
while left < len(t) and s[left] == t[left]:
left += 1
if left == len(t):
return True
right = len(t) - 1
while right >= 0 and s[right + 1] == t[right]:
right -= 1
if right == -1:
return True
return left == right + 1
```