1930. Unique Length-3 Palindromic Subsequences

LeetCodeHash TableStringBit ManipulationPrefix SumOpen on judge ↗

Given a string s, return the number of unique palindromes of length three that are a subsequence of s. Note that even if there are multiple ways to obtain the same subsequence, it is still only counted once. A palindrome is a string that reads the same forwards and backwards. A subsequence of a string is a new string generated from the original string with some characters (can be none) deleted

HINT LADDERno hints yet

L1 Observation

L2 Technique

L3 Approach

L4 Pseudo-code

🔒

L5 Full solution

L5 unlocks only if you insist twice

solution.cppC++17

CodeSearch Tutor

Hints, not spoilers — it won’t hand over the full solution unless you insist.

voice by Sarvam AI