Separate the Digits in an Array - Practice Coding Problems

Separate the Digits in an Array - Problem

Array Simulation Easy

Given an array of positive integers, your task is to separate each number into its individual digits and return a new array containing all these digits in the same order they appear.

Think of it like taking apart a stack of multi-digit numbers and laying out each digit individually. For example, if you have the number 1234, you would separate it into [1, 2, 3, 4].

Goal: Transform an array of integers into an array of their constituent digits.
Input: An array of positive integers
Output: An array of digits maintaining the original order

Example: [13, 25, 83, 77] becomes [1, 3, 2, 5, 8, 3, 7, 7]

Input & Output

example_1.py — Basic Case

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

› Output: [1, 3, 2, 5, 8, 3, 7, 7]

💡 Note: Each number is broken into its digits: 13→[1,3], 25→[2,5], 83→[8,3], 77→[7,7]

example_2.py — Single Digits

$ Input: nums = [7, 1, 3, 9]

› Output: [7, 1, 3, 9]

💡 Note: Single-digit numbers remain unchanged as they have only one digit each

example_3.py — Mixed Lengths

$ Input: nums = [1, 234, 56, 7890]

› Output: [1, 2, 3, 4, 5, 6, 7, 8, 9, 0]

💡 Note: Numbers of different lengths: 1→[1], 234→[2,3,4], 56→[5,6], 7890→[7,8,9,0]

Constraints

1 ≤ nums.length ≤ 1000
1 ≤ nums[i] ≤ 10⁵
All integers are positive

Visualization

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Understanding the Visualization

Input Processing

Take each number from the input array

String Conversion

Convert the number to string format for easy digit access

Digit Extraction

Extract each character and convert back to integer

Result Building

Add each digit to the result array in order

Key Takeaway

🎯 Key Insight: String conversion provides the simplest way to access individual digits, making the code readable and maintainable while achieving optimal time complexity.

Asked in

a Amazon 25 G Google 18 ⊞ Microsoft 12 f Meta 8

The optimal approach uses string conversion to easily access individual digits. Convert each number to a string, iterate through each character, and convert back to integers. This gives us O(n × d) time complexity where d is the average number of digits, making it efficient and intuitive.

Common Approaches

Approach	Time	Space	Notes
✓ String Conversion Approach	O(n * d)	O(n * d)	Convert each number to string and extract digits character by character

String Conversion Approach — Algorithm Steps

Initialize an empty result array
For each number in the input array
Convert the number to a string
For each character in the string
Convert character back to integer and add to result
Return the result array

Visualization

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Step-by-Step Walkthrough

Input Array

Start with array of integers [13, 25, 83, 77]

Convert to String

Convert first number 13 to string '13'

Extract Digits

Extract '1' and '3', convert to integers 1, 3

Continue Process

Repeat for remaining numbers

Code -

solution.c — C

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int* separateDigits(int* nums, int numsSize, int* returnSize) {
    // Estimate result size (max 10 digits per number)
    int* result = malloc(numsSize * 10 * sizeof(int));
    int resultIndex = 0;
    
    for (int i = 0; i < numsSize; i++) {
        // Convert number to string
        char str[12];  // enough for 32-bit int
        sprintf(str, "%d", nums[i]);
        
        // Process each digit character
        for (int j = 0; str[j] != '\0'; j++) {
            result[resultIndex++] = str[j] - '0';
        }
    }
    
    *returnSize = resultIndex;
    return result;
}

int main() {
    int nums[] = {13, 25, 83, 77};
    int returnSize;
    int* result = separateDigits(nums, 4, &returnSize);
    
    printf("[");
    for (int i = 0; i < returnSize; i++) {
        printf("%d", result[i]);
        if (i < returnSize - 1) printf(", ");
    }
    printf("]\n");
    
    free(result);
    return 0;
}

Time & Space Complexity

Time Complexity

⏱️

O(n * d)

Where n is the number of integers and d is the average number of digits per integer

✓ Linear Growth

Space Complexity

O(n * d)

For storing the result array and temporary string representations

⚡ Linearithmic Space

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Input & Output

Constraints

Visualization

Related Problems

Common Approaches

String Conversion Approach — Algorithm Steps

Visualization

Code -

Time & Space Complexity

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