Remove Palindromic Subsequences

Description

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.

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: String is already palindrome

Example 2:

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

Example 3:

Input: s = "baabb"
Output: 2
Explanation: "baabb" -> "b" -> "". 
Remove palindromic subsequence "baab" then "b".

Example 4:

Input: s = ""
Output: 0

 

Constraints:

• 0 <= s.length <= 1000
• s only consists of letters 'a' and 'b'

Solution(javascript)

/**
 * @param {string} s
 * @return {number}
 */
const removePalindromeSub = function (s) {
  const isPalindrome = () => {
    let i = 0
    let j = s.length - 1
    while (i <= j) {
      if (s[i] !== s[j]) {
        return false
      }
      i += 1
      j -= 1
    }
    return true
  }
  if (s.length === 0) {
    return 0
  }
  if (isPalindrome(s)) {
    return 1
  }
  return 2
}