# Snail Trail Problem in JavaScript

Suppose we have an array like this −

const arr = [
[1, 2, 3, 4],
[12,13,14,5],
[11,16,15,6],
[10,9, 8, 7]
];

The array is bound to be a square matrix.

We are required to write a JavaScript function that takes in this array and constructs a new array by taking elements and spiraling in until it converges to center. A snail trail spiraling around the outside of the matrix and inwards.

Therefore, the output for the above array should be −

const output = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16];

Therefore, let’s write the code for this function. We will solve this problem using recursion.

## Example

The code for this will be −

const arr = [
[1, 2, 3, 4],
[12,13,14,5],
[11,16,15,6],
[10,9, 8, 7]
];
const spiralForm = arr => {
return arr.length > 1 ?
arr.splice(0,1)[0]
.concat(spiralForm(arr[0].map((c, i) => {
return arr.map(r => r[i]);
})
.reverse())) :
arr[0]
}
console.log(spiralForm(arr));

## Output

The output in the console will be −

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

Updated on: 22-Oct-2020

186 Views