/** * @param {number[]} nums * @return {boolean} */ var containsDuplicate = function(nums) { const map = {}; for (let num of nums) { if (num in map) return true; map[num] = num; } return false; }; var containsDuplicateSet = function(nums) { return new Set(nums).size !== nums.length; }; containsDuplicate([1,2,3,4,5,1]);