Permutations II

Problem Description

Given a collection of numbers, nums, that might contain duplicates, return all possible unique permutations in any order.

Example 1:

Input: nums = [1,1,2]
Output:
[[1,1,2],
 [1,2,1],
 [2,1,1]]

Example 2:

Input: nums = [1,2,3]
Output: [[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]]

Constraints:

• 1 <= nums.length <= 8
• -10 <= nums[i] <= 10

Solution (JavaScript)

/**
 * @param {number[]} nums
 * @return {number[][]}
 */
var permuteUnique = function(nums) {
    const permu = (perm, left, rst) => {
        if(!left.length){
            rst.push(perm);
        } else {
            let prev;
            left.forEach((l, i) => {
                if(l !== prev) {
                    let newPerm = perm.slice();
                    newPerm.push(l);
                    let newLeft = left.slice();
                    newLeft.splice(i,1)
                    permu(newPerm, newLeft, rst);    
                }
                prev = l;
            });
        }
    }
    
    let rst = [];
    nums.sort();
    permu([], nums, rst);
    return rst;
};