Permutations

• Description: https://leetcode.com/problems/permutations/
• Inspired by: https://levelup.gitconnected.com/find-all-permutations-of-a-string-in-javascript-af41bfe072d2

let findPermutations = (string) => {
  if (!string || typeof string !== "string") {
    return "Please enter a string";
  } else if (string.length < 2) {
    return string;
  }

  let permutationsArray = [];

  for (let i = 0; i < string.length; i++) {
    let char = string[i];

    let remainingChars =
      string.slice(0, i) + string.slice(i + 1, string.length);

    for (let permutation of findPermutations(remainingChars)) {
      permutationsArray.push(char + permutation);
    }
  }
  return permutationsArray;
};

const permute = (nums) => {
  if (nums < 2) {
    return [nums];
  }
  const permutationsArray = [];

  for (let i = 0; i < nums.length; i++) {
    const num = nums[i];
    const remainingNums = [
      ...nums.slice(0, i),
      ...nums.slice(i + 1, nums.length),
    ];
    for (const permutation of permute(remainingNums)) {
      permutationsArray.push([num, ...permutation]);
    }
  }
  return permutationsArray;
};
/**
 *
 * 输入：nums = [1,2,3]
 * 输出：[[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]]
 */
console.log(permute([1, 2, 3]));