Simple 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:\nO(n)\n\n- Space complexity:\nO(n)\n\n# Code\n```\n/**\n * @param {number[]} nums\n * @return {number}\n */\nvar findMaxK = function(nums) {\n    res=-1\n    let seen=new Set()\n    for(const num of nums){\n        if(seen.has(-num)){\n            res=Math.max(res,Math.abs(num))\n        }\n        seen.add(num)\n    }\n   \n    return res\n    \n};\n```
['JavaScript']