2023.11.14 Today's Challenge

https://leetcode.com/problems/unique-length-3-palindromic-subsequences/

Unique Length-3 Palindromic Subsequences - LeetCode

무식하게 구하면 TL이 나올 듯.
slice를 잘 해서 구현하는 방법이 있음

class Solution:
    def countPalindromicSubsequence(self, s: str) -> int:
        letters = set(s)
        ans = 0

        for letter in letters:
            i, j = s.index(letter), s.rindex(letter)
            between = set()

            for k in range(i+1, j):
                between.add(s[k])
            
            ans += len(between)
        
        return ans