Merge pull request #781 from dancinghui/master

加入python版本的双指针解法

problems/0005.最长回文子串.md

@@ -288,7 +288,34 @@ class Solution:
         return s[left:right + 1]
 
 ```
+> 双指针法：
+```python
+class Solution:
+    def longestPalindrome(self, s: str) -> str:
 
+        def find_point(i, j, s):
+            while i >= 0 and j < len(s) and s[i] == s[j]:
+                i -= 1
+                j += 1
+            return i + 1, j
+
+        def compare(start, end, left, right):
+            if right - left > end - start:
+                return left, right
+            else:
+                return start, end
+
+        start = 0
+        end = 0
+        for i in range(len(s)):
+            left, right = find_point(i, i, s)
+            start, end = compare(start, end, left, right)
+
+            left, right = find_point(i, i + 1, s)
+            start, end = compare(start, end, left, right)
+        return s[start:end]
+
+```
 ## Go
 
 ```go