1332. Remove Palindromic Subsequences

Question

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.

Solution

当字符为空时，返回0。
注意本题中的子序列不需要连续。
由于只有’a’与’b’两个字符，因此最多两步即可将字符串清空。

辅助方法判断字符串是否为回文字符串。
如果为真则返回1，只需要删除一次。

如果为假则返回2，需要先删除所有的’a’，再删除所有的’b’。

Code

class Solution {
    public int removePalindromeSub(String s) {
        if(s.length() == 0) return 0;
        return isPalindrome(s) ? 1 : 2;
    }
    
    private boolean isPalindrome(String s){
        int i = 0, j = s.length() - 1;
        while(j > i){
            if(s.charAt(i) != s.charAt(j)) return false;
            i++;
            j--;
        }
        return true;
    }
}