Snail Traversal

Problem Statement

The task is to develop a method named snail that transforms a one-dimensional array into a two-dimensional array arranged in a specific order known as snail traversal order. This method should be applicable universally to modify how arrays behave in your code. It should accept rowsCount and colsCount as parameters to determine the dimensions of the resulting two-dimensional array.

The transformation should only happen if the product of rowsCount and colsCount matches the length of the one-dimensional array (nums). If this condition isn't met, or any other input is invalid, the method should return an empty array.

Snail traversal order is an arrangement starting from the top-left of the array and proceeding vertically downwards through the entire first column, then moving to the next column to the right and continuing upwards, alternating the direction with each subsequent column to the left. This continues until the entire array is traversed.

Examples

Example 1

Input:

nums = [19, 10, 3, 7, 9, 8, 5, 2, 1, 17, 16, 14, 12, 18, 6, 13, 11, 20, 4, 15]
rowsCount = 5
colsCount = 4

Output:

[
[19,17,16,15],
 [10,1,14,4],
 [3,2,12,20],
 [7,5,18,11],
 [9,8,6,13]
]

Example 2

Input:

nums = [1,2,3,4]
rowsCount = 1
colsCount = 4

Output:

[[1, 2, 3, 4]]

Example 3

Input:

nums = [1,3]
rowsCount = 2
colsCount = 2

Output:

[]

Explanation:

2 multiplied by 2 is 4, and the original array [1,3] has a length of 2; therefore, the input is invalid.

Constraints

• 0 <= nums.length <= 250
• 1 <= nums[i] <= 1000
• 1 <= rowsCount <= 250
• 1 <= colsCount <= 250

Approach and Intuition

To solve the problem of converting a 1D array to a 2D snail order array, an understanding of array operations and simple mathematical checks for validating inputs is needed. Here is a step-by-step breakdown based on the examples provided:

1. Verification of Validity:

   • First, check if the product of rowsCount and colsCount equals the length of the array. If not, return an empty array since the transformation cannot be accurately performed.

2. Initialization:

   • If the input is valid, initialize a 2D array with rowsCount rows and colsCount columns.

3. Traversal Setup:

   • Determine the traversal dynamics. You'll need variables to control your position in the original array and to decide when to switch the direction of traversal (downward or upward through columns).

4. Filling the 2D Array:

   • Start filling the 2D array by picking elements from the 1D array. Begin at the top-left corner and proceed downward until the end of the column, then switch to the next column and proceed upward, and so forth.
   • Continue this pattern until all elements from the 1D array are placed in the 2D array.

5. Edge Cases Handling:

   • Always have checks in place for corner cases such as arrays of length zero, or extremely large values of rowsCount or colsCount (within allowed constraints).

By following the above approach, you can ensure that any 1D array provided with appropriate dimensions can be correctly transformed into its snail order 2D counterpart.

Solutions

Array.prototype.snailFill = function(height, width) {
    if (height * width !== this.length) return [];
        
    const output = new Array(height).fill().map(() => new Array(width).fill());
    
    const moves = [[1, 0], [-1, 0]]; // down, up
    let currentDirection = 0;
    let currentRow = 0;
    let currentCol = 0;
    
    for (let index = 0; index < this.length; index++) {
        output[currentRow][currentCol] = this[index];
        let newRow = currentRow + moves[currentDirection][0];
        let newCol = currentCol;
    
        if (newRow < 0 || newRow == height) {
            currentDirection = (currentDirection + 1) % 2; // toggle direction
            newRow = currentRow;
            newCol = currentCol + 1;
        }
    
        currentRow = newRow;
        currentCol = newCol;
    }
    
    return output;
}