solved palindromic-substrings

Author: sun912

palindromic-substrings/sun912.py

@@ -0,0 +1,26 @@
+"""
+    TC: O(n^2)
+
+    TC in first try was O(n^3).
+    It is the improved codes from neetcodes
+    key point is that each character in loop is considered to middle one.
+    Ant then, check left end and right end.
+
+"""
+class Solution:
+    def countSubstrings(self, s: str) -> int:
+        result = 0
+        for i in range(len(s)):
+            result += self.countPalindrom(s, i, i)
+            result += self.countPalindrom(s, i, i+1)
+        return result
+
+
+    def countPalindrom(self, s, left_end, right_end):
+        result = 0
+        while left_end >= 0 and right_end < len(s) and s[left_end] == s[right_end]:
+            result += 1
+            left_end -= 1
+            right_end += 1
+
+        return result