How Can I Generate All Permutations of an Integer Array in JavaScript?

Permutation Generation in JavaScript

To generate permutations of an array of integers in JavaScript, a recursive function can be employed. The aim is to take an integer array as input, and return an array containing all possible permutations, each with the same length as the input array.

Modified Permutation Function

The provided function for string permutation can be modified by considering the differences in how methods operate on integers and strings:

const permArr = [];
const usedNums = [];

function permuteIntegers(input) {
  for (let i = 0; i < input.length; i++) {
    const num = input.splice(i, 1)[0];
    usedNums.push(num);
    if (input.length === 0) {
      permArr.push([...usedNums]);
    }
    permuteIntegers(input);
    input.splice(i, 0, num);
    usedNums.pop();
  }
  return permArr;
}

Shorter and Modern Version (ES6)

Using modern JavaScript features, the above function can be simplified:

const permutator = (inputArr) => {
  const result = [];

  const permute = (arr, memo = []) => {
    if (arr.length === 0) {
      result.push(memo);
    } else {
      for (let i = 0; i < arr.length; i++) {
        const curr = arr.slice();
        const next = curr.splice(i, 1)[0];
        permute(curr, memo.concat(next));
      }
    }
  };

  permute(inputArr);
  return result;
};

Usage Examples

Both functions can be used to generate permutations of integer arrays:

console.log(permuteIntegers([1, 2, 3])); // Output: [[1, 2, 3], [1, 3, 2], [2, 1, 3], [2, 3, 1], [3, 1, 2], [3, 2, 1]]

console.log(permutator([1, 2, 3])); // Output: same as above

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