LeetCode-in-All

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

class Solution {
    fun permute(nums: IntArray): List<List<Int>> {
        if (nums.isEmpty()) {
            return ArrayList()
        }
        val finalResult: MutableList<List<Int>> = ArrayList()
        permuteRecur(nums, finalResult, ArrayList(), BooleanArray(nums.size))
        return finalResult
    }

    private fun permuteRecur(
        nums: IntArray,
        finalResult: MutableList<List<Int>>,
        currResult: MutableList<Int>,
        used: BooleanArray
    ) {
        if (currResult.size == nums.size) {
            finalResult.add(ArrayList(currResult))
            return
        }
        for (i in nums.indices) {
            if (used[i]) {
                continue
            }
            currResult.add(nums[i])
            used[i] = true
            permuteRecur(nums, finalResult, currResult, used)
            used[i] = false
            currResult.removeAt(currResult.size - 1)
        }
    }
}

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