Watch 10 video solutions for Separate the Digits in an Array, a easy level problem involving Array, Simulation. This walkthrough by Learn to Code has 1,174 views views. Want to try solving it yourself? Practice on FleetCode or read the detailed text solution.
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.
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 <= 10001 <= nums[i] <= 105Problem Overview: You receive an array of positive integers. For every number, split it into its individual digits and append those digits to a result array while preserving the original order. For example, [13, 25] becomes [1, 3, 2, 5]. The challenge is simply extracting digits efficiently while keeping the sequence correct.
This problem falls under basic Array traversal and Simulation. You process each number one by one and simulate digit extraction.
Approach 1: String Conversion Method (O(n·k) time, O(n·k) space)
The simplest implementation converts each number into a string, then iterates over its characters. Each character represents a digit, so convert it back to an integer and append it to the result list. If n is the number of integers and k is the average number of digits per integer, the algorithm performs roughly n × k operations.
This approach is popular because it is extremely readable and avoids manual digit manipulation. Most high-level languages provide fast string iteration, so the performance is usually more than sufficient for interview constraints. The tradeoff is extra temporary memory used by the string representation, which makes the space complexity O(n·k) including the output.
Approach 2: Mathematical Division Method (O(n·k) time, O(n·k) space)
This method extracts digits using arithmetic instead of string operations. For each number, repeatedly apply num % 10 to obtain the last digit and num / 10 to remove it. Because this produces digits in reverse order, store them temporarily (for example in a stack or small list) and then append them back to the result in reverse.
The algorithm still processes every digit exactly once, so the time complexity remains O(n·k). Space complexity is also O(n·k) due to the output plus a small temporary buffer per number. This approach is useful when you want tighter control over numeric operations or when avoiding string conversions is preferred.
Recommended for interviews: Both approaches are acceptable because the complexity is identical. The string conversion solution demonstrates clean thinking and quick implementation, which interviewers appreciate for an easy problem. The mathematical division method shows deeper understanding of digit manipulation and is sometimes preferred in lower-level environments where avoiding string conversion matters.
| Approach | Time | Space | When to Use |
|---|---|---|---|
| String Conversion Method | O(n·k) | O(n·k) | Best for readability and fast implementation in interviews |
| Mathematical Division Method | O(n·k) | O(n·k) | When avoiding string conversion or demonstrating numeric digit extraction |