121-Best-Time-to-Buy-and-Sell-Stock.js

/**
 * https://leetcode.com/problems/best-time-to-buy-and-sell-stock/description/
 * Difficulty:Easy
 *
 * Say you have an array for which the ith element is the price of a given stock on day i.
 * If you were only permitted to complete at most one transaction
 * (ie, buy one and sell one share of the stock), design an algorithm to find the maximum profit.
 *
 * Example 1:
 * Input: [7, 1, 5, 3, 6, 4]
 * Output: 5
 * max. difference = 6-1 = 5 (not 7-1 = 6, as selling price needs to be larger than buying price)
 *
 * Example 2:
 * Input: [7, 6, 4, 3, 1]
 * Output: 0
 * In this case, no transaction is done, i.e. max profit = 0.
 */

/**
 * @param {number[]} prices
 * @return {number}
 */
var maxProfit = function (prices) {
    if (!prices.length) return 0;
    var min = prices[0];
    var max = 0;
    for (var i = 1; i < prices.length; i++) {
        var tmp = prices[i];
        if (tmp < min) min = tmp;
        else if (tmp - min > max) max = tmp - min;
    }
    return max;

};

console.log(maxProfit([7, 1, 5, 3, 6, 4]));
console.log(maxProfit([7, 6, 4, 3, 1]));