/**

* Difficulty:

* Medium

*

* Desc:

* Given a collection of numbers that might contain duplicates, return all possible unique permutations.

*

* Example:

* [1,1,2] have the following unique permutations:

* [

* [1,1,2],

* [1,2,1],

* [2,1,1]

* ]

*

* 还是排列组合，但是数组内可能会有重复的数字。

* 所以看见这题我是懵逼的，因为它的要求其实就是我在写 46 题时专门注意的点，即处理数组内的重复数字。

* (所以说其实 46 题不用考虑处理重复数字的问题？？)

* 直接用 46 题的代码直接 AC...

*/

var treeLayer = function(nums, path, layer, results, usedSet) {

var pre = null;

for (var i = 0; i < nums.length; i += 1) {

var num = nums[i];

var key = `${i}-${num}`;

var set;

if (!usedSet) {

set = new Set();

} else {

set = new Set([...usedSet]);

}

if (set.has(key)) {

continue;

}

if (pre === null) {

pre = num;

} else if (pre === num) {

continue;

}

set.add(key);

pre = num;

var p = [...path, num];

if (p.length === nums.length) {

results.push(p);

} else {

treeLayer(nums, p, layer + 1, results, set);

}

}

};

/**

* @param {number[]} nums

* @return {number[][]}

*/

var permuteUnique = function(nums) {

nums.sort((a, b) => a - b);

var results = [];

treeLayer(nums, [], 0, results);

return results;

};