1332. Remove Palindromic Subsequences

LeetCode 1332. Remove Palindromic Subsequences

Description

You are given a string s consisting only of letters 'a' and 'b'. In a single step you can remove one palindromic subsequence from s.

Return the minimum number of steps to make the given string empty.

A string is a subsequence of a given string if it is generated by deleting some characters of a given string without changing its order. Note that a subsequence does not necessarily need to be contiguous.

A string is called palindrome if is one that reads the same backward as well as forward.

Example 1:

Input: s = "ababa"
Output: 1
Explanation: s is already a palindrome, so its entirety can be removed in a single step.

Example 2:

Input: s = "abb"
Output: 2
Explanation: "abb" -> "bb" -> "". 
Remove palindromic subsequence "a" then "bb".

Constraints:

• 1 <= s.length <= 1000

• s[i] is either 'a' or 'b'.

Tags

String

Solution

• Return 0 if it's an empty string;

• Return 1 if it's a palindrome string;

• Return 2, because what we need to remove are substrings. We can remove all a then all b.

Complexity

• Time complexity: $O(n)$

• Space complexity: $O(n)$

Code

func removePalindromeSub(s string) int {
	if len(s) == 0 {
		return 0
	}
	for l, r := 0, len(s)-1; l < r; l, r = l+1, r-1 {
		if s[l] != s[r] {
			return 2
		}
	}
	return 1
}