sliding window problems

Author: MMJLee

longest_repeat_char_replace.py

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+class LongestRepeatCharReplace():
+    def longest_repeat_char_replace(self, str: str, k: int) -> int:
+        count = {}
+        res = 0
+        left = 0
+        maxF = 0
+        # basically trying to find the longest repeating substring but k values can be different
+        for right in range(len(str)):
+            # dict counting freq of characters
+            count[str[right]] = 1 + count.get(str[right], 0)
+            maxF = max(maxF, count[str[right]])
+            # (right - left + 1) - maxF is the # of characters that need to be replaced
+            while (right - left + 1) - maxF > k:
+                # start decrementing frequencies of characters as left index starts moving
+                count[str[left]] -= 1
+                left += 1
+            res = max(res, right - left + 1)
+        return res

longest_repeat_char_replace_test.py

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+# https://leetcode.com/problems/longest-repeating-character-replacement/
+from longest_repeat_char_replace import LongestRepeatCharReplace
+
+tester = LongestRepeatCharReplace()
+
+
+def test_general_case_one():
+    assert tester.longest_repeat_char_replace("abab", 2) == 4
+
+
+def test_replace_one():
+    assert tester.longest_repeat_char_replace("aababba", 1) == 4
+
+
+def test_no_replacements():
+    assert tester.longest_repeat_char_replace("pwwkew", 0) == 2

longest_substring_no_repeat.py

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+# https://leetcode.com/problems/longest-substring-without-repeating-characters/
+class LongestSubstringNoRepeat():
+    def longest_substring_no_repeat(self, str: str) -> int:
+        charSet = set()  # {} is dict
+        max_length = 0
+        left = 0
+        for curr in range(len(str)):
+            # repeat (removing char at left index and incrementing) until val at curr index is not in set
+            while str[curr] in charSet:
+                charSet.remove(str[left])
+                left += 1
+            charSet.add(str[curr])
+            max_length = max(max_length, curr - left + 1)
+        return max_length

longest_substring_no_repeat_test.py

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+# https://leetcode.com/problems/longest-substring-without-repeating-characters/
+
+from longest_substring_no_repeat import LongestSubstringNoRepeat
+
+tester = LongestSubstringNoRepeat()
+
+
+def test_general_case():
+    assert tester.longest_substring_no_repeat("abcabcbb") == 3
+
+
+def test_single_letter():
+    assert tester.longest_substring_no_repeat("bbbbb") == 1
+
+
+def test_advance_left_by_two():
+    assert tester.longest_substring_no_repeat("pwwkew") == 3