Separate the Digits in an Array

Separate the Digits in an Array - Problem

Array Simulation Easy

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].

Input & Output

Example 1 — Basic Case

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

› Output: [1,3,2,5,8,3]

💡 Note: Separate digits: 13 → [1,3], 25 → [2,5], 83 → [8,3]. Combine: [1,3,2,5,8,3]

Example 2 — Single Digits

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

› Output: [7,1,3,9]

💡 Note: Single digit numbers remain unchanged: [7,1,3,9]

Example 3 — Larger Numbers

$ Input: nums = [1000,23]

› Output: [1,0,0,0,2,3]

💡 Note: 1000 → [1,0,0,0], 23 → [2,3]. Combined: [1,0,0,0,2,3]

Constraints

1 ≤ nums.length ≤ 1000
1 ≤ nums[i] ≤ 10⁵

Visualization

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Asked in

a Amazon 15 G Google 12

The key insight is to process each number digit by digit. The most intuitive approach uses string conversion to easily access individual digits. Time: O(n × d), Space: O(n × d) where d is average digits per number.

Common Approaches

✓ Mathematical Digit Extraction

⏱️ Time: O(n × d) Space: O(n × d)

Extract digits using mathematical operations: repeatedly divide by 10 and use modulo to get each digit. This avoids string conversion overhead.

String Conversion

⏱️ Time: O(n × d) Space: O(n × d)

For each number in the array, convert it to a string and iterate through each character to extract individual digits. Convert each digit character back to integer and add to result.

Mathematical Digit Extraction — Algorithm Steps

For each number, extract digits using modulo and division operations
Collect digits in reverse order, then reverse the list
Add all digits to result array

Visualization

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Step-by-Step Walkthrough

Extract Digits

Use modulo 10 to get last digit, divide by 10 to remove it

Reverse Order

Digits come out in reverse, so we reverse them

Combine All

Add all digits to result array

Code -

solution.c — C

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

int* solution(int* nums, int numsSize, int* returnSize) {
    int* result = malloc(10000 * sizeof(int)); // Max possible digits
    int resultIndex = 0;
    
    for (int i = 0; i < numsSize; i++) {
        // Extract digits using mathematical operations
        int digits[20];
        int digitCount = 0;
        int temp = nums[i];
        
        while (temp > 0) {
            digits[digitCount++] = temp % 10;
            temp /= 10;
        }
        
        // Digits are in reverse order, so add them in reverse
        for (int j = digitCount - 1; j >= 0; j--) {
            result[resultIndex++] = digits[j];
        }
    }
    
    *returnSize = resultIndex;
    return result;
}

int main() {
    char line[10000];
    fgets(line, sizeof(line), stdin);
    
    // Parse JSON array manually
    int nums[1000];
    int numsSize = 0;
    char* ptr = strchr(line, '[') + 1;
    char* token = strtok(ptr, ",]");
    while (token != NULL) {
        nums[numsSize++] = atoi(token);
        token = strtok(NULL, ",]");
    }
    
    int returnSize;
    int* result = solution(nums, numsSize, &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 array length and d is average number of digits per number

✓ Linear Growth

Space Complexity

O(n × d)

Result array stores all digits from all numbers

⚡ Linearithmic Space

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Input & Output

Constraints

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Related Problems

Common Approaches

Mathematical Digit Extraction — Algorithm Steps

Visualization

Code -

Time & Space Complexity

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