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Leetcode 2553. Separate the Digits in an Array

Problem Statement

You are given an integer array nums. The purpose of the function is to:

1. Convert each number in the array nums to its constituent digits.
2. Return the array of these digits in the same order as they appeared in the original numbers.

Clarifying Questions

1. Input Constraints: What is the range of values for the integers in the input array?
   • Clarification: We assume integers can be both positive or negative, and the array can be of reasonable size to fit into memory.
2. Output Format: How should the digits of the original numbers be ordered in the output array?
   • Clarification: Digits of each number should appear in the same order as they appear when the number is read from left to right.

Strategy

1. Initialize an Output Array: Start with an empty vector to hold the resulting digits.
2. Iterate Through Each Number: Convert each number to a string to easily access each digit.
3. Extract and Store Digits: For each character (digit) in the string representation, convert it back to an integer and push it onto the output array.
4. Return the Output Array: After processing all numbers, return the resulting array.

Time Complexity

• O(n * m): Where n is the number of elements in the input array and m is the average number of digits in the numbers. Each number is converted to a string and each digit is processed individually.

Here is the corresponding C++ code:

#include <vector>
#include <string>

std::vector<int> separateDigits(const std::vector<int>& nums) {
    std::vector<int> result;
    for (int num : nums) {
        std::string numStr = std::to_string(num);
        for (char digit : numStr) {
            if(digit == '-') continue; // Skip negative sign
            result.push_back(digit - '0');
        }
    }
    return result;
}

Explanation

• Initialization: std::vector<int> result; prepares an empty vector to store the digits.
• Conversion: std::string numStr = std::to_string(num); converts each number to its string representation.
• Digit Extraction: The inner loop for (char digit : numStr) iterates through each character of the string. We ignore the negative sign if present.
• Storing Digits: result.push_back(digit - '0'); converts the character to its integer form and adds it to the result array.
• The function finally returns the result vector containing all the digits in the required order.

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