First Missing Positive

Given an unsorted integer array, find the smallest missing positive integer. Note: Your algorithm should run in O(n) time and use constant extra space.

Sounds hard right?

var firstMissingPositive = function(nums) { if (nums.length <= 1) return nums[0] == 1 ? 2 : 1; const max = Math.max(...nums); for (let i = 1; i <= max + 1; i++) { if (!nums.includes(i)) return i; //alternatively: if (nums.indexOf(i) === -1) return i; } return 1; //every other case, ie all n in nums are < 0 }; 

// Runtime: 48 ms, faster than 95.76% of JavaScript online submissions for First Missing Positive.
// Memory Usage: 33.8 MB, less than 91.67% of JavaScript online submissions for First Missing Positive.