Problem

You have a bomb to defuse, and your time is running out! Your informer will provide you with a circular array code of length of n and a key k.

To decrypt the code, you must replace every number. All the numbers are replaced simultaneously.

  • If k > 0, replace the ith number with the sum of the next k numbers.
  • If k < 0, replace the ith number with the sum of the previous k numbers.
  • If k == 0, replace the ith number with 0.

As code is circular, the next element of code[n-1] is code[0], and the previous element of code[0] is code[n-1].

Given the circular array code and an integer key k, return the decrypted code to defuse the bomb!

Examples

Example 1:

Input: code = [5,7,1,4], k = 3
Output: [12,10,16,13]
Explanation: Each number is replaced by the sum of the next 3 numbers. The decrypted code is [7+1+4, 1+4+5, 4+5+7, 5+7+1]. Notice that the numbers wrap around.

Example 2:

Input: code = [1,2,3,4], k = 0
Output: [0,0,0,0]
Explanation: When k is zero, the numbers are replaced by 0.

Example 3:

Input: code = [2,4,9,3], k = -2
Output: [12,5,6,13]
Explanation: The decrypted code is [3+9, 2+3, 4+2, 9+4]. Notice that the numbers wrap around again. If k is negative, the sum is of the **previous** numbers.

Solution

Method 1 - Using Sliding window

Code

Java
class Solution {
    public int[] decrypt(int[] code, int k) {
        int n = code.length;
        int[] ans = new int[n];
        
        if (k == 0) {
            return ans;
        }
        
        if (k > 0) {
            for (int i = 0; i < n; i++) {
                int sum = 0;
                for (int j = 1; j <= k; j++) {
                    sum += code[(i + j) % n];
                }
                ans[i] = sum;
            }
        } else { // k < 0
            k = -k;
            for (int i = 0; i < n; i++) {
                int sum = 0;
                for (int j = 1; j <= k; j++) {
                    sum += code[(i - j + n) % n];
                }
                ans[i] = sum;
            }
        }
        
        return ans;
    }
}
Python
class Solution:
    def decrypt(self, code: List[int], k: int) -> List[int]:
        n = len(code)
        ans = [0] * n
        
        if k == 0:
            return ans
        
        if k > 0:
            for i in range(n):
                ans[i] = sum(code[(i + j) % n] for j in range(1, k + 1))
        else:  # k < 0
            for i in range(n):
                ans[i] = sum(code[(i + j) % n] for j in range(k, 0))
        
        return ans

Complexity

  • ⏰ Time complexity: O(n * |k|) where n is the length of the array and |k| is the absolute value of k.
  • 🧺 Space complexity: O(n) for the resultant array ans.