Enhancement for gavinfish#1

Author: gavinfish

python/005 Longest Palindromic Substring.py

@@ -2,8 +2,9 @@
 Given a string S, find the longest palindromic substring in S. You may assume that the maximum length of S is 1000, and there exists one unique longest palindromic substring.
 '''
 
+
 class Solution(object):
-    def longestPalindrome(self, s):
+    def longestPalindrome2(self, s):
         """
         :type s: str
         :rtype: str
@@ -21,7 +22,8 @@ def longestPalindrome(self, s):
         m = 0
         # Length of the current substring
         c = 0
-        #  Whether the substring contains the first character or last character and is palindromic
+        # Whether the substring contains the first character or last character
+        # and is palindromic
         b = True
         for i in range(0, n):
             # Odd situation
@@ -50,6 +52,26 @@ def longestPalindrome(self, s):
             b = True
         return s[l:r]
 
+    def longestPalindrome(self, s):
+        string = "#" + "#".join(s) + "#"
+        i = 0
+        maxBorder = 0  # store the max border that has been reached
+        maxCenter = 0  # the center of palindrome that has been largest for now
+        p = [0 for _ in range(len(string))]  # min in (center to i or i to border)
+        res = [0, 0]
+
+        while i < len(string):
+            p[i] = min(p[2 * maxCenter - i], maxBorder - i) if maxBorder > i else 1
+            while i - p[i] >= 0 and i + p[i] < len(string) and string[i - p[i]] == string[i + p[i]]:
+                p[i] += 1
+            if maxBorder < p[i] + i:
+                maxBorder = p[i] + i
+                maxCenter = i
+                if maxBorder - maxCenter > res[1] - res[0]:
+                    res = [maxCenter, maxBorder]
+            i += 1
+
+        return "".join([x for x in string[2 * res[0] - res[1] + 1:res[1]] if x != '#'])
 
 
 if __name__ == "__main__":