1115 revise

020. Valid Parentheses.py

@@ -5,7 +5,7 @@ class Solution(object):
     def isValid(self, s):
         """
         O(N)
-        O(1)
+        O(N)
         :type s: str
         :rtype: bool
         """

647. Palindromic Substrings.py

@@ -0,0 +1,35 @@
+# Given a string, your task is to count how many palindromic substrings in this string.
+
+# The substrings with different start indexes or end indexes are counted as different substrings even they consist of same characters.
+
+# Example 1:
+# Input: "abc"
+# Output: 3
+# Explanation: Three palindromic strings: "a", "b", "c".
+# Example 2:
+# Input: "aaa"
+# Output: 6
+# Explanation: Six palindromic strings: "a", "a", "a", "aa", "aa", "aaa".
+# Note:
+# The input string length won't exceed 1000.
+class Solution(object):
+    def countSubstrings(self, s):
+        """
+        :type s: str
+        :rtype: int
+        """
+        if not s:
+            return 0
+        if len(s) == 1:
+            return 1
+
+        count = [0]
+        for i in range(len(s)):
+            self.check(s,i,i,count) # abcddcba  -- # abcdcba
+            self.check(s,i,i+1, count)
+        return count[0]
+    def check(self, s, l, r, count):
+        while l>=0 and r < len(s) and s[l] == s[r]:
+            count[0] += 1
+            l -= 1
+            r += 1