func permute(_ nums: [Int]) -> [[Int]] {
        var res = [[Int]]()
        var visited = [Bool](repeating: false, count: nums.count)
        get(&res, [], &visited, nums)
        return res
    }
    func get(_ res: inout [[Int]], _ cur:[Int], _ visited: inout [Bool] , _ nums: [Int]){
        guard cur.count < nums.count else {
            res.append(cur)
            return 
        }
        for i in 0 ..< nums.count where !visited[i]{
            visited[i] = true
            get(&res, cur + [nums[i]], &visited, nums)
            visited[i] = false
        }
    }