Add 'Permutation in String'

Author: nickolashkraus

README.md

@@ -64,6 +64,8 @@ A collection of LeetCode solutions
 
 [Minimum Size Subarray Sum](./src/minimum_size_subarray_sum.py)
 
+[Permutation in String](./src/permutation_in_string.py)
+
 [Product of Array Except Self](./src/product_of_array_except_self.py)
 
 [Remove Nth Node From End of List](./src/remove_nth_node_from_end_of_list.py)

src/permutation_in_string.py

@@ -0,0 +1,68 @@
+"""
+567. Permutation in String
+
+https://leetcode.com/problems/permutation-in-string
+
+NOTES
+  * Use a sliding window.
+
+I tried to get fancy with this one and use bitwise operations. This failed.
+Just use a hash map or, better still, an array of size 26 (one index for each
+character).
+"""
+
+from collections import Counter
+
+
+class Solution:
+    def checkInclusion(self, s1: str, s2: str) -> bool:
+        left, right = 0, len(s1)
+
+        # Create a mapping of character -> frequency. Here, it is advantageous
+        # to use an instance of Counter, however an ordinary dict would work
+        # just as well.
+        s1_counter: Counter[str] = Counter(s1)
+        s2_counter: Counter[str] = Counter(s2[: len(s1)])
+
+        while right < len(s2):
+            if s1_counter == s2_counter:
+                return True
+            s2_counter[s2[right]] += 1
+            right += 1
+            s2_counter[s2[left]] -= 1
+            left += 1
+
+        # Add final equality check.
+        return s1_counter == s2_counter
+
+
+class ArraySolution:
+    def checkInclusion(self, s1: str, s2: str) -> bool:
+        def offset(c: str) -> int:
+            return ord(c) - ord("a")
+
+        left, right = 0, len(s1)
+
+        # Use an array of size 26. NOTE: In order to offset a character so that
+        # it is between 0 and 25, use:
+        #
+        #   ord(c) - ord('a')
+        s1_counter: list[int] = [0] * 26
+        s2_counter: list[int] = [0] * 26
+
+        for i in range(len(s1)):
+            s1_counter[offset(s1[i])] += 1
+
+        for i in range(len(s1)):
+            s2_counter[offset(s2[i])] += 1
+
+        while right < len(s2):
+            if s1_counter == s2_counter:
+                return True
+            s2_counter[offset(s2[right])] += 1
+            right += 1
+            s2_counter[offset(s2[left])] -= 1
+            left += 1
+
+        # Add final equality check.
+        return s1_counter == s2_counter

tests/test_permutation_in_string.py

@@ -0,0 +1,45 @@
+"""
+567. Permutation in String
+
+https://leetcode.com/problems/permutation-in-string
+"""
+
+from unittest import TestCase
+
+from src.permutation_in_string import ArraySolution, Solution
+
+
+class TestSolution(TestCase):
+    def test_1(self):
+        exp = True
+        assert Solution().checkInclusion("ab", "eidbaooo") == exp
+
+    def test_2(self):
+        exp = False
+        assert Solution().checkInclusion("ab", "eidboaoo") == exp
+
+    def test_3(self):
+        exp = False
+        assert Solution().checkInclusion("hello", "ooolleoooleh") == exp
+
+    def test_4(self):
+        exp = False
+        assert Solution().checkInclusion("dd", "rroogzkdktk") == exp
+
+
+class TestArraySolution(TestCase):
+    def test_1(self):
+        exp = True
+        assert ArraySolution().checkInclusion("ab", "eidbaooo") == exp
+
+    def test_2(self):
+        exp = False
+        assert ArraySolution().checkInclusion("ab", "eidboaoo") == exp
+
+    def test_3(self):
+        exp = False
+        assert ArraySolution().checkInclusion("hello", "ooolleoooleh") == exp
+
+    def test_4(self):
+        exp = False
+        assert ArraySolution().checkInclusion("dd", "rroogzkdktk") == exp