Merge pull request #22 from miguelHx/miguel_1.5_one_away

Miguel 1.5 - One Away [Python]

Author: fvntr

Python/chapter01/1.5 - OneAway/miguel_1.5_sol.py

@@ -0,0 +1,84 @@
+"""
+Python version 3.7.0
+1.5 - One Away
+There are three types of edits that can be performed on strings:  insert a character,
+remove a character, or replace a character.  Given two strings, write a function to check
+if they are one edit (or zero edits) away.
+"""
+import unittest
+from typing import Callable
+
+
+def one_away(s1: str, s2: str) -> bool:
+    """
+    Checks if two strings are one edit or zero edits away.
+    There are 3 types of edits:
+    1. insert a character
+    2. remove a character
+    3. replace a character
+    Zero edits away means the two strings are exactly the same.
+    We will do different checks depending on the size different of the strings.
+    Runtime:  O(n), where n is length of s1
+    Space Complexity:  O(n + n +/- 1) = O(n), where n is length of s1
+    :param s1: one string we want to compare
+    :param s2: other string to compare
+    :return: true if one or zero edits away, false otherwise
+    """
+    # if size differs by more than 1, guaranteed more than one edit distance.
+    if abs(len(s1) - len(s2)) > 1:
+        return False
+    # if size is the same, scan for edits
+    if len(s1) == len(s2):
+        edits = 0
+        for i, c in enumerate(s1):
+            if c == s2[i]:
+                continue
+            edits += 1
+            if edits > 1:
+                return False
+        return True
+    # otherwise, we have an insertion/deletion
+    # compare both strings for insertion/deletion
+    # want to loop through the shorter string to avoid going out of bounds
+    s_short = s1 if len(s1) < len(s2) else s2
+    s_long = s1 if len(s1) > len(s2) else s2
+
+    added = 0
+    for i, c in enumerate(s_short):
+        if c == s_long[i + added]:
+            continue
+        # chars didn't match, will check next char in next iteration
+        added += 1
+        if added > 1:
+            # added more than once, and we did not match characters.
+            # guaranteed at least 2 edit distance
+            return False
+    return True
+
+
+class TestOneAwayFunction(unittest.TestCase):
+    def _run_tests(self, f: Callable[[str, str], bool]) -> None:
+        cases = [
+            ("pale", "ple", True),
+            ("pales", "pale", True),
+            ("pale", "bale", True),
+            ("pale", "bake", False),
+            ("", "swag", False),
+            ("paale", "pale", True),
+            ("a", "", True),
+            ("", "b", True),
+            ("a", "b", True),
+            ("", "", True),
+            ("pale", "elap", False),
+            ("pale", "elaps", False),
+            ("pale", "palse", True)
+        ]
+        for s1, s2, expected in cases:
+            self.assertEqual(f(s1, s2), expected, msg=(s1, s2))
+
+    def test_one_away(self):
+        self._run_tests(one_away)
+
+
+if __name__ == '__main__':
+    unittest.main()