best-time-to-buy-and-sell-stock.js

/**
 * Best Time to Buy and Sell Stock
 *
 * Say you have an array for which the i-th element is the price of a given stock on day i.
 *
 * If you were only permitted to complete at most one transaction (i.e., buy one and sell one share of the stock),
 * design an algorithm to find the maximum profit.
 *
 * Note that you cannot sell a stock before you buy one.
 *
 * Example 1:
 *
 * Input: [7,1,5,3,6,4]
 * Output: 5
 * Explanation: Buy on day 2 (price = 1) and sell on day 5 (price = 6), profit = 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
 * Explanation: In this case, no transaction is done, i.e. max profit = 0.
 */

/**
 * @param {number[]} prices
 * @return {number}
 */
const maxProfit = prices => {
  if (!prices) {
    return 0;
  }

  let profit = 0;
  let min = prices[0];

  for (let i = 1; i < prices.length; i++) {
    profit = Math.max(profit, prices[i] - min);
    min = Math.min(min, prices[i]);
  }

  return profit;
};

export { maxProfit };