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01/05.py

+'''
+	Given a string s, find the longest palindromic substring in s. You may assume that the maximum length of s is 1000.
+
+	Example 1:
+
+	Input: "babad"
+	Output: "bab"
+	Note: "aba" is also a valid answer.
+	Example 2:
+
+	Input: "cbbd"
+	Output: "bb"
+'''
+
+class Solution(object):
+    def longestPalindrome(self, s):
+        """
+        :type s: str
+        :rtype: str
+        """
+        dp = [[0 for _ in range(len(s))] for _ in range(len(s))]
+        maxLength, result = 1, ""
+        for index in range(len(s)):
+        	dp[index][index] = 1
+        	result = s[index]
+
+        length = 2
+        
+        while length <= len(s):
+        	index_i = 0
+        	while index_i < len(s) - length + 1:
+        		index_j = index_i + length -1
+
+        		if length == 2 and s[index_i] == s[index_j]:
+        			dp[index_i][index_j] = 1
+        			maxLength = max(maxLength, 2)
+        			result = s[index_i:index_j+1]
+        		elif s[index_i] == s[index_j] and dp[index_i+1][index_j-1]:
+        			dp[index_i][index_j] = 1
+        			if length > maxLength:
+        				maxLength = length
+        				result = s[index_i:index_j+1]
+
+        		index_i += 1
+        	length += 1
+
+        return result
+
+# Space: O(N^2)
+# Time: O(N^2)
+
+class Solution(object):
+    def longestPalindrome(self, s):
+        """
+        :type s: str
+        :rtype: str
+        """
+
+        def expand(s, left, right):
+        	while left >= 0 and right < len(s) and s[left] == s[right]:
+        		left -= 1
+        		right += 1
+        	return right-left-1
+
+        start, end = 0, 0
+        for index in range(len(s)):
+        	even_len = expand(s, index, index+1)
+        	odd_len = expand(s, index, index)
+        	length = max(even_len, odd_len)
+        	if length > (end-start):
+        		start = index - (length-1)/2
+        		end = index +length/2
+
+        return s[start:end+1]
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