subsets

def subsets(self, nums):
        solution = [[]]
        if len(nums) == 0:
            return solution
        sorted_list = sorted(nums) #to simplify, we sort input array
        for k in range(1,len(nums)+1):
            init_set,traverse_stack = [i for i in range(k)],[] #note solution here store position index instead of member of input array since input array is not necessarily be [1..n]
            last_solution = init_set[:]
            solution.append([sorted_list[i] for i in last_solution])
            for pos in range(k-1,-1,-1):
                traverse_stack.append(pos)
                while len(traverse_stack) != 0:
                    if last_solution[traverse_stack[-1]] + k - traverse_stack[-1] <= len(nums)-1:
                        while last_solution[traverse_stack[-1]] + k - traverse_stack[-1] <= len(nums)-1:
                            tpos = traverse_stack[-1]
                            last_solution[tpos] += 1
                            for x in range(tpos+1,k):
                                last_solution[x] = last_solution[x-1] + 1
                                traverse_stack.append(x)
                            solution.append([sorted_list[i] for i in last_solution])
                    else:
                        traverse_stack.pop()
        return solution
 #see comments
 
 recursive version:
 def subsets_recursive(self, nums, solution_set, combo, x):
        if combo not in solution_set:
            solution_set.append(combo[:])
        
        for element in range(x,len(nums)):
            combo.append(nums[element])
            self.subsets_recursive(nums,solution_set,combo,element+1)
            combo.pop()
            
    def subsets(self, nums):
        solution_set, combo = [], []
        self.subsets_recursive(nums,solution_set,combo,0)
        return solution_set