1652. Defuse the Bomb

1652. Defuse the Bomb

Difficulty: Easy

Topics: Array, Sliding Window

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!

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.

Constraints:

• n == code.length


• 1 <= n <= 100


• 1 <= code[i] <= 100


• -(n - 1) <= k <= n - 1

Hint:

1. As the array is circular, use modulo to find the correct index.


2. The constraints are low enough for a brute-force solution.

Solution:

We can implement a function that iterates over the code array and computes the sum of the appropriate numbers based on the value of k.

The general approach will be as follows:

1. If k == 0, replace all elements with 0.


2. If k > 0, replace each element with the sum of the next k elements in the circular array.


3. If k < 0, replace each element with the sum of the previous k elements in the circular array.

The circular nature of the array means that for indices that exceed the bounds of the array, you can use modulo (%) to "wrap around" the array.

Let's implement this solution in PHP: 1652. Defuse the Bomb

<?php

/**

 * @param Integer[] $code

 * @param Integer $k

 * @return Integer[]

 */

function decrypt($code, $k) {

    ...

    ...

    ...

    /**

     * go to ./solution.php

     */

}



// Example Usage

$code1 = [5, 7, 1, 4];

$k1 = 3;

print_r(decrypt($code1, $k1)); // Output: [12, 10, 16, 13]



$code2 = [1, 2, 3, 4];

$k2 = 0;

print_r(decrypt($code2, $k2)); // Output: [0, 0, 0, 0]



$code3 = [2, 4, 9, 3];

$k3 = -2;

print_r(decrypt($code3, $k3)); // Output: [12, 5, 6, 13]

?>

Explanation:

1. 
   

   Initialization:

   
   
   
   
   
   • We create a result array initialized with zeros using array_fill.
   
   
   
   


2. 
   

   Handling k == 0:

   
   
   
   
   
   • If k is zero, the output array is simply filled with zeros, as required by the problem.
   
   
   
   


3. 
   

   Iterating Through the Array:

   
   
   
   
   
   • For each index i in the array:
     
     
     
     
     • If k > 0, sum the next k elements using modulo arithmetic to wrap around.
     
     
     • If k < 0, sum the previous |k| elements using modulo arithmetic with an offset to handle negative indices.
     
     
     
     
   
   
   
   


4. 
   

   Modulo Arithmetic:

   
   
   
   
   
   • We use ($i + $j) % $n to wrap around to the beginning of the array when accessing indices greater than n - 1.
   
   
   • Similarly, ($i - $j + $n) % $n handles backward wrapping for negative indices.
   
   
   
   


5. 
   

   Complexity:

   
   
   
   
   
   • Time Complexity: O(n . |k|), where n is the size of the array and |k| is the absolute value of k.
   
   
   • Space Complexity: O(n) for the result array.
   
   
   
   

Outputs:

The provided examples match the expected results. Let me know if you need further explanation or optimizations!

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