[python]longest-palindromic-substring

src/leetcode/00005.longest-palindromic-substring/5-1.py

@@ -0,0 +1,21 @@
+class Solution:
+    def longestPalindrome(self, s: str) -> str:
+        res = s[0]
+        for i in range(len(s)):
+            for j in range(i + 1, len(s)):
+                if j - i + 1 > len(res) and self.check(s, i, j):
+                    res = s[i : j + 1]
+        return res
+
+    def check(self, s, i, j):
+        while i < j:
+            if s[i] != s[j]:
+                return False
+            i += 1
+            j -= 1
+        return True
+
+
+if __name__ == "__main__":
+    print(Solution().longestPalindrome("babad"))
+    print(Solution().longestPalindrome("cbbd"))

src/leetcode/00005.longest-palindromic-substring/5-2.py

@@ -0,0 +1,30 @@
+class Solution:
+    """
+    ## P(i,j)
+
+    1. i == j => true
+    2. j - i <= 2 => s[i] == s[j]
+    3. j -i > 2=> s[i] == s[j] && P(i+1,j-1)
+    """
+
+    def longestPalindrome(self, s: str) -> str:
+        res = s[0]
+        length = len(s)
+        arr = [[False for _ in range(length)] for _ in range(length)]
+        for i in range(len(s) - 1, -1, -1):
+            for j in range(i + 1, len(s)):
+                if i == j:
+                    arr[i][j] = True
+                elif j - i <= 2:
+                    arr[i][j] = s[i] == s[j]
+                else:
+                    arr[i][j] = (s[i] == s[j]) and arr[i + 1][j - 1]
+                if arr[i][j] and j - i + 1 > len(res):
+                    res = s[i : j + 1]
+        return res
+
+
+if __name__ == "__main__":
+    # print(Solution().longestPalindrome("babad"))
+    # print(Solution().longestPalindrome("cbbd"))
+    print(Solution().longestPalindrome("abcba"))

src/leetcode/00005.longest-palindromic-substring/5-3.py

@@ -0,0 +1,23 @@
+class Solution:
+    def __init__(self):
+        self.res = ""
+
+    def longestPalindrome(self, s: str) -> str:
+        self.res = s[0]
+
+        for i in range(len(s)):
+            self.work(s, i, i)
+            self.work(s, i, i + 1)
+        return self.res
+
+    def work(self, s, left, right):
+        while left >= 0 and right < len(s) and s[left] == s[right]:
+            left -= 1
+            right += 1
+        if right - left - 1 > len(self.res):
+            self.res = s[left + 1 : right]
+
+
+if __name__ == "__main__":
+    print(Solution().longestPalindrome("babad"))
+    print(Solution().longestPalindrome("cbbd"))