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 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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Understanding the Visualization

Input Array

Array of positive integers

Separate Digits

Extract each digit from every number

Output Array

Flattened array of individual digits

Key Takeaway

🎯 Key Insight: Convert each number to string or use mathematical operations to extract digits in order

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

Approach	Time	Space	Notes
✓ String Conversion	O(n × d)	O(n × d)	Convert each number to string and extract digits
Mathematical Digit Extraction	O(n × d)	O(n × d)	Use mathematical operations to extract digits without string conversion

String Conversion — Algorithm Steps

Iterate through each number in the input array
Convert number to string
Extract each digit character and convert back to integer
Add all digits to the result array

Visualization

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Step-by-Step Walkthrough

Convert to String

Each number becomes a string of characters

Extract Digits

Each character is converted back to integer

Combine Results

All digits are collected in order

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++) {
        // Convert number to string to access individual digits
        char numStr[20];
        sprintf(numStr, "%d", nums[i]);
        
        for (int j = 0; j < strlen(numStr); j++) {
            // Convert digit character back to integer
            result[resultIndex++] = numStr[j] - '0';
        }
    }
    
    *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

Visualization

Related Problems

Common Approaches

String Conversion — Algorithm Steps

Visualization

Code -

Time & Space Complexity

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