ThirdMaximumNumber.js

// Source : https://leetcode.com/problems/third-maximum-number
// Author : Dean Shi
// Date   : 2020-04-17

/***************************************************************************************
 * Given a non-empty array of integers, return the third maximum number in this array.
 * If it does not exist, return the maximum number. The time complexity must be in O(n).
 * 
 * Example 1:
 * Input: [3, 2, 1]
 * 
 * Output: 1
 * 
 * Explanation: The third maximum is 1.
 * 
 * Example 2:
 * Input: [1, 2]
 * 
 * Output: 2
 * 
 * Explanation: The third maximum does not exist, so the maximum (2) is returned
 * instead.
 * 
 * Example 3:
 * Input: [2, 2, 3, 1]
 * 
 * Output: 1
 * 
 * Explanation: Note that the third maximum here means the third maximum distinct
 * number.
 * Both numbers with value 2 are both considered as second maximum.
 * 
 * 
 ***************************************************************************************/

/**
 * @param {number[]} nums
 * @return {number}
 */
var thirdMax = function(nums) {
    const list = []

    for (let num of new Set(nums)) {
        list.push(num)
        list.sort((a, b) => b - a)

        if (list.length > 3) {
            list.pop()
        }
    }

    return list.length === 3 ? list.pop() : list.shift()
};