2553. Separate the Digits in an Array

2553. Separate the Digits in an Array

Difficulty: Easy

Topics: Mid Level, Array, Simulation, Biweekly Contest 97

Given an array of positive integers nums, return an array answer that consists of the digits of each integer in nums after separating them in the same order they appear in nums.

To separate the digits of an integer is to get all the digits it has in the same order.

• For example, for the integer 10921, the separation of its digits is [1,0,9,2,1].

Example 1:

• Input: nums = [13,25,83,77]
• Output: [1,3,2,5,8,3,7,7]
• Explanation:
  • The separation of 13 is [1,3].
  • The separation of 25 is [2,5].
  • The separation of 83 is [8,3].
  • The separation of 77 is [7,7].
  • answer = [1,3,2,5,8,3,7,7]. Note that answer contains the separations in the same order.

Example 2:

• Input: nums = [7,1,3,9]
• Output: [7,1,3,9]
• Explanation:
  • The separation of each integer in nums is itself.
  • answer = [7,1,3,9].

Constraints:

• 1 <= nums.length <= 1000
• 1 <= nums[i] <= 10⁵

Hint:

1. Convert each number into a list and append that list to the answer.
2. You can convert the integer into a string to do that easily.

Solution:

The problem requires taking an array of positive integers and returning a new array that contains the individual digits of each number, in the original order of numbers and digits.

The solution uses string conversion to split each number into its digits, then appends those digits to the result array.

Approach:

• Iterate through each integer in the input array.
• Convert each integer to a string to easily access each character (digit).
• Split the string into an array of characters.
• Convert each character back to an integer and append it to the result array.
• Return the final array of digits.

Let's implement this solution in PHP: 2553. Separate the Digits in an Array

<?php
/**
 * @param Integer[] $nums
 * @return Integer[]
 */
function separateDigits(array $nums): array
{
    ...
    ...
    ...
    /**
     * go to ./solution.php
     */
}

// Test cases
print_r(separateDigits([13,25,83,77])) . "\n";          // Output: [1,3,2,5,8,3,7,7]
print_r(separateDigits([7,1,3,9])) . "\n";              // Output: [7,1,3,9]
?>

Explanation:

• Step 1: Initialize an empty array $answer to hold the final digits.
• Step 2: Loop through each number $num in $nums.
• Step 3: Convert $num to a string and split it into individual characters using str_split().
• Step 4: Loop through each character in the split array, cast it to an integer, and push it to $answer.
• Step 5: After processing all numbers, return $answer.

Complexity

• Time Complexity: O(n * m), where n is the number of integers in nums and m is the maximum number of digits in any integer (up to 6 digits since nums[i] ≤ 10⁵).
• Space Complexity: O(total digits) for the output array, which is the sum of digits across all numbers in nums.
• Efficiency: The approach is optimal because we must output each digit exactly once.

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