1332. Remove Palindromic Subsequences

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

class Solution {
    public int removePalindromeSub(String s) {
        if(s.length() == 0) return 0;
        return isPal(s) ? 1 : 2;
    }
    public boolean isPal(String s){
        int l = 0, r = s.length() - 1;
        while(l <= r){
            if(s.charAt(l) != s.charAt(r)) return false;
            l++;
            r--;
        }
        return true;
    }
}

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注意是subsequence，意思是可以随便取隔着取。所以如果本来是palindrome就返回1，如果不是就先取a再取b返回2