longest palindromic substring . leetcode Q5

0005/README.md

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+# Longest Palindromic Substring
+
+### Problem statemen
+Given a string s, return the longest palindromic substring in s.

0005/longest_palindromic_substring.py

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+def longestPalindrome(self, s):
+    res = ""
+    for i in xrange(len(s)):
+        # odd case, like "aba"
+        tmp = self.helper(s, i, i)
+        if len(tmp) > len(res):
+            res = tmp
+        # even case, like "abba"
+        tmp = self.helper(s, i, i+1)
+        if len(tmp) > len(res):
+            res = tmp
+    return res
+
+# get the longest palindrome, l, r are the middle indexes   
+# from inner to outer
+def helper(self, s, l, r):
+    while l >= 0 and r < len(s) and s[l] == s[r]:
+        l -= 1; r += 1
+    return s[l+1:r]