O(n) Time, O(1) Space Solution
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```\npublic class Solution {\n    public int FindMaxK(int[] nums) {\n        int[] pair = new int[1001];\n        int max = -1;\n        for (int i = 0; i < nums.Length; i++)\n        {\n            if (Math.Sign(nums[i]) == -1)\n            {\n                if (pair[nums[i] * -1] == nums[i] * -1)\n                {\n                    max = Math.Max(max, nums[i] * -1);\n                }\n                else\n                {\n                    pair[nums[i] * -1] = nums[i];\n                }\n            }\n            else\n            {\n                if (pair[nums[i]] == nums[i] * -1)\n                {\n                    max = Math.Max(max, nums[i]);\n                }\n                else\n                {\n                    pair[nums[i]] = nums[i];\n                }\n            }\n        }\n        return max;\n    }\n}\n```
['C#']