1323. Maximum 69 Number (easy)

Q:

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'

A:

就是存入一个list里，然后找第一个 
（NOTE: should not use vector, as we need insert at the begining, can use std::deque. or std:list )

class Solution {
public:
    int maximum69Number (int num) {
        std::list<int> list;
        while(num>0)
        {
            int r = num%10;
            num /= 10;
            list.push_front(r);
        }
        bool flipped = false;
        int res = 0;
        for(auto v:list)
        {
            if(v==6 && !flipped)
            {
                v = 9;
                flipped = true;
            }
            res = res*10 + v;
        }
        return res;
    }
};