# Why do you use a Deque in the non-recursive solution?

In the task Permutations (medium), the non-recursive solution looks like this:

``````const Deque = require('./collections/deque'); //http://www.collectionsjs.com

function find_permutations(nums) {
let numsLength = nums.length,
result = [],
permutations = new Deque();
permutations.push([]);
for (let i = 0; i < nums.length; i++) {
const currentNumber = nums[i];
// we will take all existing permutations and add the current number to create new permutations
const n = permutations.length;
for (let p = 0; p < n; p++) {
const oldPermutation = permutations.shift();
// create a new permutation by adding the current number at every position
for (let j = 0; j < oldPermutation.length + 1; j++) {
const newPermutation = oldPermutation.slice(0); // clone the permutation
newPermutation.splice(j, 0, currentNumber); // insert currentNumber at index 'j'
if (newPermutation.length === numsLength) {
result.push(newPermutation);
} else {
permutations.push(newPermutation);
}
}
}
}

return result;
}
``````

Could you please explain why a Deque is necessary when a Queue or (for JS) a simple array would do the job just fine?