3324. Find the Sequence of Strings Appeared on the Screen

You are given a string target.

Alice is going to type target on her computer using a special keyboard that has only two keys:

• Key 1 appends the character "a" to the string on the screen.
• Key 2 changes the last character of the string on the screen to its next character in the English alphabet. For example, "c" changes to "d" and "z" changes to "a".

Note that initially there is an empty string "" on the screen, so she can only press key 1.

Return a list of all strings that appear on the screen as Alice types target, in the order they appear, using the minimum key presses.

Example 1:

Input: target = "abc"

Output: ["a","aa","ab","aba","abb","abc"]

Explanation:

The sequence of key presses done by Alice are:

• Press key 1, and the string on the screen becomes "a".
• Press key 1, and the string on the screen becomes "aa".
• Press key 2, and the string on the screen becomes "ab".
• Press key 1, and the string on the screen becomes "aba".
• Press key 2, and the string on the screen becomes "abb".
• Press key 2, and the string on the screen becomes "abc".

Example 2:

Input: target = "he"

Output: ["a","b","c","d","e","f","g","h","ha","hb","hc","hd","he"]

Constraints:

• 1 <= target.length <= 400
• target consists only of lowercase English letters.

Solution:

// class Solution {
//     public List<String> stringSequence(String target) {

//         List<String> result = new ArrayList<String>();
//         StringBuilder sb = new StringBuilder();
//         for (int i = 0; i < target.length(); i++){
//             char cur = target.charAt(i);
//             char start = 'a';
//             sb.append(start);
//             result.add(sb.toString());

//             while(start != cur){
//                 start++;
//                 sb.replace(i, )

//             }
//         }
//     }
// }
class Solution {
    public List<String> stringSequence(String target) {
        List<String> result = new ArrayList<>();
        StringBuilder screen = new StringBuilder();

        for (char targetChar : target.toCharArray()) {
            // Step 1: Press key 1 to add 'a' to the current string
            screen.append('a');
            result.add(screen.toString());  // Add the string after appending 'a'

            // Step 2: Change the last character to match the target character
            while (screen.charAt(screen.length() - 1) != targetChar) {
                // Press Key 2 to change the last character
                char lastChar = screen.charAt(screen.length() - 1);
                lastChar = lastChar == 'z' ? 'a' : (char)(lastChar + 1);  // Loop from 'z' to 'a'
                screen.setCharAt(screen.length() - 1, lastChar);
                result.add(screen.toString());  // Add each intermediate state
            }
        }

        return result;
    }
}


/*

    key1: -> "a"
    key2: next alphabet

    Note that initially there is an empty string "" on the screen, so she can only press key 1.
    -> start from a 

    Return a list of all strings that appear on the screen as Alice types target, in the order they appear, using the minimum key presses.
    minimum key presses 

    he -> a



 */