Adding challenge 5.

Author: badprog

p_5_longest_palindromic_substring/README.md

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+# p_5_longest_palindromic_substring
+
+🔗 https://leetcode.com/problems/longest-palindromic-substring/description/?source=submission-noac
+
+## Leetcode - 5 - Longest palindromic substring
+
+Given a string s, return the longest palindromic substring in s.
+
+Example 1:
+
+Input: s = "babad"  
+Output: "bab"  
+Explanation: "aba" is also a valid answer.
+
+Example 2:
+
+Input: s = "cbbd"  
+Output: "bb"
+
+Constraints:
+
+1 <= s.length <= 1000
+s consist of only digits and English letters.

p_5_longest_palindromic_substring/src/__init__.py

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+# https://github.com/badprog/badprog_leetcode_python
+
+################
+# import
+import sys
+import pathlib
+
+# Adding the parent directory of this file to the sys.path
+sys.path.append(str(pathlib.Path(__file__).resolve().parents[1]))
+
+from src.solution import Solution
+from typing import List
+
+################
+#
+def main():
+    print("Hello from Badprog, Leetcode challenge 5 and Rust :D")
+    solution = Solution()
+    s = "abracadabra"
+    result = solution.longestPalindrome(s)
+    print("result = {}", result)
+    
+################
+#
+if __name__ == "__main__":
+    main()
+

p_5_longest_palindromic_substring/src/main.py

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+# https://github.com/badprog/badprog_leetcode_python
+
+############################
+#
+class Solution:
+    ############################
+    #
+    def longestPalindrome(self, s: str) -> str:
+        # 1
+        special_char = '#'
+        str_ready = special_char.join(s)
+        str_ready = special_char + str_ready + special_char
+        
+        # 2
+        str_len = len(str_ready)
+        vec_palindrom = [0] * str_len
+        # print(f"str_len: {str_len}, vec_palindrom:{vec_palindrom}")
+        palindrom_center = 0
+        palindrom_right = 0
+        
+        # 3
+        for (index, element) in enumerate(str_ready):
+            # print(f"index: {index}, element: {element}")
+            if index < palindrom_right:
+                vec_palindrom[index] = min(palindrom_right - index, vec_palindrom[2 * palindrom_center - index])
+            else:
+                vec_palindrom[index] = 0
+                
+            # 4
+            while   (index + vec_palindrom[index] + 1 < str_len and 
+                    index - vec_palindrom[index] -1 >= 0 and 
+                    str_ready[index - vec_palindrom[index] - 1] == 
+                    str_ready[index + vec_palindrom[index] + 1]):
+                vec_palindrom[index] += 1
+                
+            # 5
+            if index + vec_palindrom[index] > palindrom_right:
+                palindrom_center = index
+                palindrom_right = index + vec_palindrom[index]
+            
+        # 6
+        # max_center = max(int(char) for char in vec_palindrom if char.isdigit())
+        max_center = max(vec_palindrom)
+        max_index = vec_palindrom.index(max_center)
+        # print(f"vec_palindrom: {vec_palindrom}")
+        # print(f"max_center: {max_center}")
+        # print(f"max_index: {max_index}")
+        start = (max_index - max_center) // 2
+        # print(f"start: {start}")
+        end = start + max_center
+        
+        str_to_return = s[start:end]
+        # print(f"str_to_return: {str_to_return}")
+
+        # return        
+        return str_to_return
+    

p_5_longest_palindromic_substring/src/solution.py

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+# https://github.com/badprog/badprog_leetcode_python
+
+############################
+# import
+import sys
+import pathlib
+
+# Adding the parent directory of this file to the sys.path
+sys.path.append(str(pathlib.Path(__file__).resolve().parents[1]))
+
+import pytest
+from src.solution import Solution
+
+@pytest.mark.parametrize("input_str, expected", [
+    ("babad", {"bab", "aba"}),
+    ("cbbd", {"bb"}),
+    ("a", {"a"}),
+    ("racecar", {"racecar"}),
+    ("aaaa", {"aaaa"}),
+    ("abc", {"a", "b", "c"}),
+    ("", {""}),
+    ("ababa", {"ababa"}),
+    ("abcdedcba", {"abcdedcba"}),
+    ("abbcccbba", {"abbcccbba"}),
+])
+
+def test_longest_palindrome(input_str, expected):
+    solution = Solution()
+    result = solution.longestPalindrome(input_str)
+    assert result in expected, f"Failed for entry={input_str}, expected={expected}, current={result}"
+