08. Remove Palindromic Subsequences.cpp

/*
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

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

Hint #1  
Use the fact that string contains only 2 characters.

Hint #2  
Are subsequences composed of only one type of letter always palindrome strings ?
*/

class Solution
{
public:
  int removePalindromeSub(string s)
  {
    int i = 0, n = s.size(), j = s.size() - 1;
    if (n <= 1)
      return n;
    int flag = 0;
    while (i < j)
    {
      if (s[i++] != s[j--])
      {
        flag = 1;
        break;
      }
    }

    return flag == 0 ? 1 : 2;
  }
};