Is Find the Sequence of Strings Appeared on the Screen easy or hard?

The problem is generally rated Medium because it requires careful simulation and tracking of intermediate states. The algorithm itself is straightforward, but missing small steps in the process can lead to incorrect sequences.

Find the Sequence of Strings Appeared on the Screen Python/Java solution

In Python or Java, maintain a current string (or character array) and simulate the operations. Increment the last character until it equals the target character, storing each intermediate result, then append 'a' when moving to the next index. Both implementations run in O(n) effective time and O(n) space.

How to solve Find the Sequence of Strings Appeared on the Screen in O(n)?

Simulate the screen operations using a current string or character array. For each target character, repeatedly increment the last character until it matches the target, recording every intermediate state. Then append 'a' to start constructing the next position. Because each character increases at most 25 times, the total runtime is linear in the target length.

What is the best approach for Find the Sequence of Strings Appeared on the Screen?

The best approach is direct simulation of the typing process. Start with the string "a", increment the last character until it matches the target character, and append 'a' when moving to the next position. This approach runs in O(26 * n) time, effectively O(n), and uses O(n) space for storing the sequence of intermediate strings.

Is Find the Sequence of Strings Appeared on the Screen asked at Google/Amazon/Meta?

This style of problem appears in interviews at companies like Amazon, Google, and Meta when testing simulation and string manipulation skills. While the exact problem may vary, candidates are often asked to model a process step-by-step and track intermediate states efficiently.

What data structure is used in Find the Sequence of Strings Appeared on the Screen?

The core data structures are a string or a mutable character array to represent the current screen content, and a list or array to store all intermediate strings. The algorithm mainly relies on string manipulation and simple iteration.

What is the time complexity of Find the Sequence of Strings Appeared on the Screen?

The time complexity is O(26 * n), where n is the length of the target string. Each position may require up to 25 increments to reach the desired character from 'a'. Since 26 is a constant alphabet size, the complexity simplifies to O(n). Space complexity is O(n) for storing the resulting sequence of strings.

Description Hints 2 Solution Video 0:45

3324. Find the Sequence of Strings Appeared on the Screen

Medium79.5% acceptance1 company

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.

Asked at 1 company

Bloomberg

Topics

Simulation String

Hints open one at a time

Hint 1

Append the character 'a' using key 1.

Hint 2

Convert it to the required character using key 2.

0:45

Still stuck?Read 3 approaches, or watch a walkthrough.

Open solution