[leetcode - Bliend-75 ] 217. Contains Duplicate (Easy)

Given an integer array nums, return true if any value appears at least twice in the array, and return false if every element is distinct.

给定一个 nums 的阵列，如果该阵列中的数值都没有重複及回传 true 反之回传 false，这题使用 for-looｐ遍历 nums 阵列后用 hash-table 记录每个 item 出现的次数，如果出现超过 1 次则回传 false。

Example 1:

Input: nums = [1,2,3,1]
Output: true
Example 2:

Input: nums = [1,2,3,4]
Output: false
Example 3:

Input: nums = [1,1,1,3,3,4,3,2,4,2]
Output: true

Coding

var containsDuplicate = function(nums) {    const map = new Map();    for (let i = 0; i < nums.length; i++) {        if (!map.get(nums[i])) {            // if item is not exist in hash-table  -> insert into hash-table            map.set(nums[i], 1);        } else {            // item is exist in hash-table            return true;        }    }    return false;};

hash-table 的 get 为 O(1) 而 for-loop 遍历 nums 阵列为 O(n)