[bhyun-kim, 김병현] Week 11 Solutions

Author: bhyun-kim

palindromic-substrings/bhyun-kim.py

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+"""
+647. Palindromic Substrings
+https://leetcode.com/problems/palindromic-substrings/
+
+Solution:
+    To solve this problem, we can use the expand from center technique.
+    We can iterate through each character in the string and expand from the center to find palindromic substrings.
+    We can handle both odd and even length palindromes by expanding from the center and center + 1.
+    We keep track of the number of palindromic substrings found.
+    The total number of palindromic substrings is the sum of palindromic substrings found at each character.
+
+Time complexity: O(n^2)
+    - We iterate through each character in the string.
+    - For each character, we expand from the center to find palindromic substrings.
+    - The time complexity is O(n^2) due to the nested loops.
+
+Space complexity: O(1)
+    - We use constant space to store variables.
+    - The space complexity is O(1).
+"""
+
+
+class Solution:
+    def countSubstrings(self, s: str) -> int:
+        num_pal_strs = 0
+
+        def expand_from_center(left, right):
+            num_pal = 0
+            while left >= 0 and right < len(s) and s[left] == s[right]:
+                left -= 1
+                right += 1
+                num_pal += 1
+            return num_pal
+
+        for i in range(len(s)):
+            num_pal_strs += expand_from_center(i, i)
+            num_pal_strs += expand_from_center(i, i + 1)
+
+        return num_pal_strs