👨‍💻 738LeetCode

Palindromic Substrings

Question

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

Input: "abc"
Output: 3
Explanation: Three palindromic strings: "a", "b", "c"
Input: "aaa"
Output: 6
Explanation: Six palindromic strings: "a", "a", "a", "aa", "aa", "aaa"

Solution

class Solution:
    def countSubstrings(self, s: str) -> int:
        dp = [[False] * len(s) for _ in range(len(s))]
        count = []
        for j in range(len(s)):
            dp[j][j] = True
            count.append(s[j])
            for i in range(0, j):
                if j - i == 1 and s[i] == s[j]:
                    dp[i][j] = s[i] == s[j]
                    count.append(s[i:j + 1])
                else:
                    dp[i][j] = s[i] == s[j] and dp[i + 1][j - 1]
                    if dp[i][j]:
                        count.append(s[i:j + 1])
        return len(count)

Comment

Simple change from Longest Palindromic Substring Q. Instead of only saving the longest one, save all substrings.