161. One Edit Distance

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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:
  1. Insert a character into s to get t
  2. Delete a character from s to get t
  3. 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.
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Related problems
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Intuition
Corner cases when strings are null and 0 length

dfs(i, j, moves)

if (moves > 2) => return false

if chars are same => dfs(i + 1, j + 1, moves)
else dfs(i, j + 1, moves + 1) || dfs(i + 1, j + 1, moves + 1)
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