FSM + full binary tree + SortedList
Intuition\n Describe your first thoughts on how to solve this problem. \n\n# Approach\n Describe your approach to solving the problem. \n\n# Complexity\n- Time 
# Intuition\n<!-- Describe your first thoughts on how to solve this problem. -->\n\n# Approach\n<!-- Describe your approach to solving the problem. -->\n\n# Complexity\n- Time complexity:\n<!-- Add your time complexity here, e.g. $$O(n)$$ -->\n\n- Space complexity:\n<!-- Add your space complexity here, e.g. $$O(n)$$ -->\n\n# Code\n```\nclass Solution:\n    def kSum(self, nums: List[int], k: int) -> int:\n        \n\n        """\n        1: delete abs(nums[_]), 0: do not delete abs[nums[_]] from max_value\n        FSM(\u6709\u9650\u72B6\u6001\u673A) is a full binary tree\n        1\n            11\n                111\n                101\n            01\n                011\n                001\n        binary tree must satisfy:\n            1. child != father + "0"\n            2. each node at least one digit is "1"\n        """\n        from sortedcontainers import SortedList\n\n        max_value = sum(_ for _ in nums if _ > 0)\n        nums = sorted(abs(_) for _ in nums)\n        sl = SortedList([(max_value, 0)])  # sub first element\n\n        for _ in range(k):\n            v, index = sl.pop(-1)\n            if index < len(nums):\n                sl.add((v - nums[index], index + 1))\n                if index > 0:\n                    sl.add((v + nums[index - 1] - nums[index], index + 1))\n        return v\n        \n```
['Python3']