/**
 *
 * Ashish Patel
 * e: ashishsushilPatel@gmail.com
 * w: https://ashish.me
 *
 */

const permutations = nums => {
  const result = []
  const visited = new Set()
  const backtrack = curr => {
    if (nums.length == curr.length) {
      result.push([...curr])
    } else {
      for (let i = 0; i < nums.length; i++) {
        if (visited.has(i)) {
          continue
        }
        visited.add(i)
        curr.push(nums[i])
        backtrack(curr)
        visited.delete(i)
        curr.pop()
      }
    }
  }
  backtrack([])
  return result
}

const permutations3 = nums => {
  const result = []
  const backtrack = (arr, curr) => {
    if (arr.length === 0) {
      result.push(curr.slice())
      return
    }
    for (let i = 0; i < arr.length; i++) {
      const newNums = arr.slice()
      newNums.splice(i, 1)
      curr.push(arr[i])
      backtrack(newNums, curr)
      curr.pop()
    }
  }
  backtrack(nums, [])
  return result
}

const permutations2 = nums => {
  const result = []
  const backtrack = (index, combination) => {
    if (index == nums.length) {
      result.push(combination)
      return
    }
    backtrack(index + 1, [...nums[index]])
    backtrack(index + 1, [...combination, nums[index]])
  }
  backtrack(0, [])
  return result
}

console.log(permutations([1, 2, 3]))