Palindromic Substring

0647-Palindromic-Substrings.py

@@ -0,0 +1,42 @@
+'''
+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:
+    def countSubstrings(self, s: str) -> int:
+
+        def manachers(S):
+            A = '@#' + '#'.join(S) + '#$'
+            Z = [0] * len(A)
+            center = right = 0
+            for i in range(1, len(A) - 1):
+                if i < right:
+                    Z[i] = min(right - i, Z[2 * center - i])
+                while A[i + Z[i] + 1] == A[i - Z[i] - 1]:
+                    Z[i] += 1
+                if i + Z[i] > right:
+                    center, right = i, i + Z[i]
+            return Z
+
+        return sum((v + 1) // 2 for v in manachers(s))