How do you solve Separate the Digits in an Array on LeetCode?

Separate the Digits in an Array (LeetCode #2553) can be solved using Brute Force or Optimal Solution. The optimal approach is Optimal Solution with O(n) time complexity and O(n) space complexity. Key insight: Understanding how to manipulate numbers directly can be more efficient than converting to strings.

What is the brute force solution for Separate the Digits in an Array?

The brute force approach for Separate the Digits in an Array is Brute Force, with O(n²) time complexity and O(1) space complexity. The brute force approach involves converting each integer in the array to a string, then iterating through each character of the string to collect the digits. This is straightforward but can be inefficient for larger numbers due to repeated conversions. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve Separate the Digits in an Array?

Separate the Digits in an Array uses the following concepts: Array, Simulation. The recommended patterns to study are: Array, Simulation.

What are the interview tips for Separate the Digits in an Array?

Always consider the efficiency of your approach before coding. Think about how to manipulate data types directly to avoid unnecessary conversions. Practice explaining your thought process clearly, as communication is key in interviews.

What are common mistakes when solving Separate the Digits in an Array?

Forgetting to reverse the answer after extracting digits. Using string conversion unnecessarily, which can slow down the solution.

#2553

Separate the Digits in an Array

Easy

ArraySimulationArraySimulation

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

	Brute Force	Optimal Solution★
Time	O(n²)	O(n)
Space	O(1)	O(n)

💡

Intuition

Time O(n)Space O(n)

The optimal solution builds the output array directly by iterating through each number and its digits without converting to strings. This reduces overhead and improves efficiency.

⚙️

Algorithm

4 steps

1Step 1: Initialize an empty list called 'answer'.
2Step 2: For each number in the input array 'nums', repeatedly extract the last digit by taking modulo 10.
3Step 3: Append the extracted digit to 'answer' and remove the last digit by performing integer division by 10 until the number becomes 0.
4Step 4: Since digits are extracted in reverse order, reverse the 'answer' list at the end.

solution.py8 lines

1def separateDigits(nums):
2    answer = []
3    for num in nums:
4        while num > 0:
5            answer.append(num % 10)
6            num //= 10
7    answer.reverse()
8    return answer

ℹ

Complexity note: The time complexity is O(n) because we process each digit of each number exactly once. The space complexity is O(n) due to the output list storing all the digits.

1Understanding how to manipulate numbers directly can be more efficient than converting to strings.
2Reversing the order of digits is a common pattern when extracting digits from numbers.

Solutions and explanations are original Tejav content. Problem titles © LeetCode — use the LeetCode button above for the full problem statement.