2022. Convert 1D Array Into 2D Array

Difficulty: Easy

Topics: Array, Matrix, Simulation

You are given a 0-indexed 1-dimensional (1D) integer array original, and two integers, m and n. You are tasked with creating a 2-dimensional (2D) array with m rows and n columns using all the elements from original.

The elements from indices 0 to n - 1 (inclusive) of original should form the first row of the constructed 2D array, the elements from indices n to 2 * n - 1 (inclusive) should form the second row of the constructed 2D array, and so on.

Return an m x n 2D array constructed according to the above procedure, or an empty 2D array if it is impossible.

Example 1:

Input: original = [1,2,3,4], m = 2, n = 2
Output: [[1,2],[3,4]]
Explanation:
- The constructed 2D array should contain 2 rows and 2 columns.
- The first group of n=2 elements in original, [1,2], becomes the first row in the constructed 2D array.
- The second group of n=2 elements in original, [3,4], becomes the second row in the constructed 2D array.

Example 2:

Input: original = [1,2,3], m = 1, n = 3
Output: [[1,2,3]]
Explanation:
- The constructed 2D array should contain 1 row and 3 columns.
- Put all three elements in original into the first row of the constructed 2D array.

Example 3:

Input: original = [1,2], m = 1, n = 1
Output: []
Explanation:
- There are 2 elements in original.
- It is impossible to fit 2 elements in a 1x1 2D array, so return an empty 2D array.

Constraints:

1 <= original.length <= 5 * 10⁴
1 <= original[i] <= 10⁵
1 <= m, n <= 4 * 10⁴

Hint:

When is it possible to convert original into a 2D array and when is it impossible?
It is possible if and only if m * n == original.length
If it is possible to convert original to a 2D array, keep an index i such that original[i] is the next element to add to the 2D array.

Solution:

We need to follow these steps:

Check if Conversion is Possible: The conversion from a 1D array to a 2D array is only possible if the total number of elements in the 1D array (original.length) is exactly equal to m * n, where m is the number of rows and n is the number of columns. If this condition is not met, return an empty array.
Create the 2D Array: If the conversion is possible, initialize a 2D array with m rows and n columns, and populate it by iterating over the 1D array and filling in the 2D array row by row.

Let's implement this solution in PHP: 2022. Convert 1D Array Into 2D Array

<?php
/**
 * @param Integer[] $original
 * @param Integer $m
 * @param Integer $n
 * @return Integer[][]
 */
function construct2DArray($original, $m, $n) {
    ...
    ...
    ...
    /**
     * go to ./solution.php
     */
}

// Example usage:
//Example 1
$original = array(1, 2, 3, 4);
$m = 2;
$n = 2;
print_r(construct2DArray($original, $m, $n)); //Output: [[1,2],[3,4]]

//Example 2
$original = array(1, 2, 3);
$m = 1;
$n = 3;
print_r(construct2DArray($original, $m, $n)); //Output: [[1,2,3]]

//Example 3
$original = array(1, 2);
$m = 1;
$n = 1;
print_r(construct2DArray($original, $m, $n)); //Output: []
?>

Explanation:

Input Validation:
- We first calculate the length of the original array.
- If the length does not equal m * n, the conversion is impossible, and we return an empty array.
2D Array Construction:
- We initialize a 2D array named $result.
- We use a nested loop where the outer loop runs m times (for each row) and the inner loop runs n times (for each column in a row).
- We maintain an index $index that tracks our position in the original array, incrementing it as we place elements into the 2D array.

Example Output:

For the provided example:

$original = array(1, 2, 3, 4);
$m = 2;
$n = 2;
print_r(construct2DArray($original, $m, $n));

The output will be:

Array
(
    [0] => Array
        (
            [0] => 1
            [1] => 2
        )

    [1] => Array
        (
            [0] => 3
            [1] => 4
        )
)

This approach ensures that the 1D array is correctly converted into the desired 2D array, and it efficiently handles edge cases by checking whether the conversion is possible.

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