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46. Permutations

Medium

Given an array nums of distinct integers, return all the possible permutations. You can return the answer in any order.

Example 1:

Input: nums = [1,2,3]

Output: [[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]]

Example 2:

Input: nums = [0,1]

Output: [[0,1],[1,0]]

Example 3:

Input: nums = [1]

Output: [[1]]

Constraints:

• 1 <= nums.length <= 6
• -10 <= nums[i] <= 10
• All the integers of nums are unique.

Solution

object Solution {
    def permute(nums: Array[Int]): List[List[Int]] = {
        if (nums == null || nums.isEmpty) {
            return List()
        }

        val finalResult = new scala.collection.mutable.ListBuffer[List[Int]]()
        val used = Array.fill[Boolean](nums.length)(false)

        def permuteRecur(currResult: scala.collection.mutable.ListBuffer[Int]): Unit = {
            if (currResult.size == nums.length) {
                finalResult += currResult.toList
                return
            }

            for (i <- nums.indices) {
                if (!used(i)) {
                    currResult += nums(i)
                    used(i) = true
                    permuteRecur(currResult)
                    used(i) = false
                    currResult.remove(currResult.size - 1)
                }
            }
        }

        permuteRecur(new scala.collection.mutable.ListBuffer[Int]())
        finalResult.toList
    }
}

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