2553. Separate the Digits in an Array

Array
Simulation

TIME

O(d)

SPACE

O(d)

Intuition

The result must preserve both orders:

the order of numbers in nums
the left-to-right order of digits inside each number

Converting each number to a string gives the digits directly in the required order.

Approach

Initialize an empty result array.
For each number in nums:
- convert it to a string
- iterate over its characters
- convert each character back to an integer and append it
Return the result.

Complexity

Time: O(d), where d is the total number of digits across all numbers
Space: O(d), for the returned answer

Edge Cases

Single-digit numbers remain unchanged
Multi-digit numbers are expanded in-place order
Values like 100000 include zero digits in the result

Code

from typing import List


class Solution:
    def separateDigits(self, nums: List[int]) -> List[int]:
        """
        2553. Separate the Digits in an Array
        Time: O(d)
        Space: O(d)
        """
        answer = []

        for num in nums:
            for digit in str(num):
                answer.append(int(digit))

        return answer

import java.util.ArrayList;
import java.util.List;

/**
 * 2553. Separate the Digits in an Array
 * Time: O(d)
 * Space: O(d)
 */
class Solution {
    public int[] separateDigits(int[] nums) {
        List<Integer> digits = new ArrayList<>();

        for (int num : nums) {
            for (char digit : String.valueOf(num).toCharArray()) {
                digits.add(digit - '0');
            }
        }

        int[] answer = new int[digits.size()];
        for (int i = 0; i < digits.size(); i++) {
            answer[i] = digits.get(i);
        }

        return answer;
    }
}