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Leetcode 2562. Find the Array Concatenation Value

Problem Statement

You are given a 0-indexed integer array nums. The concatenation of nums is defined as follows:

• Take the first element of nums and concatenate it with the second element.
• Take the result and concatenate it with the third element, and so on until the entire array has been concatenated to form a single number.

Return the final concatenated value as an integer.

Clarifying Questions

1. Is there any limit on the size of nums?
   • Typically, constraints will be given. If not mentioned, we should assume it can be large enough to consider the algorithm’s efficiency.
2. Can nums contain negative numbers or non-integer values?
   • Typically, such problems will specify the type of elements. Assuming it’s an integer array with only non-negative numbers based on standard practices.
3. Is there a specific data type we should use for the concatenated result?
   • Given that the task is about concatenation to form a single number, handling large integers should be considered, and Java’s BigInteger might be used if values are exceptionally large.

Strategy

1. Initialization:
   • Start with an empty string or result initialized to 0.
2. Iteratively concatenate:
   • Loop through each element of the array.
   • Convert each element to a string and concatenate it to the result.
   • Convert the final concatenated string back to an integer.
3. Return the result:
   • The final concatenated value is converted to an integer (or a suitable format if it exceeds typical integer bounds).

Code

Here is the Java implementation of the described strategy:

import java.math.BigInteger;

public class Solution {
    public BigInteger findArrayConcatenationValue(int[] nums) {
        // Using StringBuilder for efficiency in concatenation
        StringBuilder concatenatedValue = new StringBuilder();
        
        // Loop through each number and concatenate
        for (int num : nums) {
            concatenatedValue.append(num);
        }
        
        // Convert the final concatenated string to BigInteger to handle large values
        BigInteger finalResult = new BigInteger(concatenatedValue.toString());
        
        return finalResult;
    }
}

Time Complexity

The time complexity of this solution is O(n), where n is the number of elements in the nums array because we loop through each element exactly once.

• Space Complexity: The space complexity is O(1) for auxiliary space, but we need O(n) space to store the concatenated result as a string.

This ensures that the solution efficiently handles the concatenation part while managing potentially large numbers using BigInteger.

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