LeetCode 651: 4 Keys Keyboard Solution

Problem Explanation

Explanation:

This problem asks us to find the maximum number of 'A's that can be printed on the screen using the following operations:

'A': Print one 'A' on the screen.
Ctrl-A: Select the whole screen.
Ctrl-C: Copy the selected text to the buffer.
Ctrl-V: Print the content of the buffer on the screen.

To solve this problem, we can use dynamic programming. We can maintain a dp array where dp[i] represents the maximum number of 'A's that can be printed with i keystrokes. At each step, we can either press 'A' or use Ctrl-A, Ctrl-C, and Ctrl-V. We can iterate through the possible number of keystrokes and calculate the maximum number of 'A's that can be printed.

Algorithm Steps:

Initialize a dp array of size n+1 to store the maximum number of 'A's that can be printed with i keystrokes.
Iterate from i=1 to n and for each i:
- Initialize dp[i] = i (press 'A' i times).
- Iterate j from i-3 down to 1 (to consider the Ctrl-A, Ctrl-C, Ctrl-V operations):
  - Update dp[i] to max(dp[i], dp[j] * (i-j-1)).

The final result will be stored in dp[n], which represents the maximum number of 'A's that can be printed with n keystrokes.

Time Complexity: The time complexity of this algorithm is O(n^2) where n is the given number of keystrokes.

Space Complexity: The space complexity is O(n) to store the dp array.

Solution Code

class Solution {
    public int maxA(int n) {
        int[] dp = new int[n + 1];
        for (int i = 1; i <= n; i++) {
            dp[i] = i;
            for (int j = i - 3; j >= 1; j--) {
                dp[i] = Math.max(dp[i], dp[j] * (i - j - 1));
            }
        }
        return dp[n];
    }
}

Frequently Asked Questions

How to solve LeetCode 651 (4 Keys Keyboard)?

This page provides optimized solutions for LeetCode problem 651 (4 Keys Keyboard) in Java, C++, and Python, along with a detailed explanation and an interactive code editor to test your code.

What is the time complexity of LeetCode 651 (4 Keys Keyboard)?

The time complexity for LeetCode 651 (4 Keys Keyboard) varies by solution. Check the detailed explanation section for specific complexities in Java, C++, and Python implementations.

Can I run code for LeetCode 651 on DevExCode?

Yes, DevExCode provides an interactive code editor where you can write, test, and run your code for LeetCode 651 in Java, C++, or Python.

651. 4 Keys Keyboard