leetcode 217

思路:本题比较简单
利用hashset,
1.从头遍历,数组,遇到重复 return true,
2.遍历完成还没return,return fasle

var containsDuplicate = function(nums) {
    const n = nums.length
    const hash = new Set()
    for (let i = 0; i < n; i++) {
        if (hash.has(nums[i])) {
            return true
        }
        hash.add(nums[i])
    }
    return false
};