LeetCode Contains Duplicates (solution)

Contains Duplicate.js

// https://leetcode.com/problems/contains-duplicate/
// this solution beats 85% of other submissions in terms of runtime, 57% in terms of memory

/**
 * @param {number[]} nums
 * @return {boolean}
 */
var containsDuplicate = function(nums) {
    const memo = {};

    for (let i = 0; i < nums.length; i++) {
        const num = nums[i];

        const seenBefore = memo[num];
        if (seenBefore) {
            return true;
        }

        memo[num] = true;
    }
    return false;
};