#2553

Easy

LeetCode Problem Workspace

Separate the Digits in an Array

Given an array of positive integers, separate each integer into its individual digits while preserving the original order in the output array.

array simulation

Problem Statement

You are given an array of positive integers nums. Your task is to return an array where each integer from nums is broken down into its individual digits, maintaining the order of appearance in nums. For example, separating 13 yields 1 and 3, which should be appended to the result in that order.

Each integer should be processed one by one, extracting digits from most significant to least significant. Construct the resulting array by appending these digits sequentially, so the final array reflects the flattened sequence of all digits from nums.

Examples

Example 1

Input: nums = [13,25,83,77]

Output: [1,3,2,5,8,3,7,7]

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]

The separation of each integer in nums is itself. answer = [7,1,3,9].

Constraints

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

Solution Approach

Iterate and Convert Each Number

Loop through nums and convert each integer into a string or list of digits. Append each digit to the result array to preserve order, leveraging the array plus simulation pattern.

Use Integer Arithmetic

Instead of string conversion, repeatedly divide each integer by 10 to extract digits in reverse, then reverse the temporary list before appending. This simulates the manual separation process efficiently.

Collect Digits Sequentially

Maintain a single output array and append digits as they are extracted from each number. This avoids extra data structures and ensures the answer matches the original order of nums.

Complexity Analysis

Metric	Value
Time	Depends on the final approach
Space	Depends on the final approach

Time complexity is O(N * D) where N is the length of nums and D is the maximum number of digits in a number. Space complexity is O(N * D) for the resulting array holding all separated digits.

What Interviewers Usually Probe

Notice the simplicity masks potential ordering errors when extracting digits.
They may hint at handling each integer individually rather than flattening all digits at once.
Be ready to discuss trade-offs between string conversion and arithmetic extraction.

Common Pitfalls or Variants

Common pitfalls

Reversing the order of digits by accident when using modulo and division without correction.
Appending digits to the wrong array or overwriting previous entries.
Ignoring single-digit numbers, which should still be included in the output array.

Follow-up variants

Separate digits for an array containing negative numbers, requiring handling of the sign.
Return the digits in reverse order for each integer while maintaining the overall array order.
Separate digits and filter out zeros or specific digits based on additional constraints.

FAQ

What is the easiest way to separate the digits in an array?

Convert each number to a string or list of digits and append them sequentially to the output array to maintain order.

Does this problem require special handling for single-digit numbers?

No, single-digit numbers are appended as-is, but they must still be included to preserve array order.

Should I use arithmetic or string conversion to separate digits?

Both approaches work; arithmetic is efficient for large numbers, while string conversion is simpler for clarity.

What is the primary pattern for this problem?

This is an array plus simulation problem, focusing on sequentially processing elements and flattening them into digits.

Can GhostInterview help avoid common pitfalls in this problem?

Yes, it highlights ordering mistakes, ensures digits are appended correctly, and confirms the final array mirrors nums accurately.

terminal

Solution

Solution 1: Simulation

Split each number in the array into digits, then put the split numbers into the answer array in order.

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class Solution:
    def separateDigits(self, nums: List[int]) -> List[int]:
        ans = []
        for x in nums:
            t = []
            while x:
                t.append(x % 10)
                x //= 10
            ans.extend(t[::-1])
        return ans

Solution 2

#### Rust

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class Solution:
    def separateDigits(self, nums: List[int]) -> List[int]:
        ans = []
        for x in nums:
            t = []
            while x:
                t.append(x % 10)
                x //= 10
            ans.extend(t[::-1])
        return ans

Continue Practicing

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