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

// 121. Best Time to Buy and Sell Stock
// You are given an array prices where prices[i] is
// the price of a given stock on the ith day.

// You want to maximize your profit by choosing a single day
// to buy one stock and choosing a different day in the future
// to sell that stock.

// Return the maximum profit you can achieve from this transaction.
// If you cannot achieve any profit, return 0.

// ---- Examples
// Input: prices = [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.
// Note that buying on day 2 and selling on day 1 is not allowed
// because you must buy before you sell.

// Input: prices = [7,6,4,3,1]
// Output: 0
// Explanation: In this case, no transactions are done and the max profit = 0.

// ---- Constraints
// Input: prices = [7,6,4,3,1]
// Output: 0
// Explanation: In this case, no transactions are done and the max profit = 0.
/**
 * @param {number[]} prices
 * @return {number}
 */
const maxProfit = function (prices) {
  let buyingPrice = prices[0];
  let maximumProfit = 0;

  for (const sellingPrice of prices) {
    // buy it as cheap as possible to realize a greater profit
    buyingPrice = Math.min(sellingPrice, buyingPrice);

    // update max profit if the current profit is greater
    maximumProfit = Math.max(maximumProfit, sellingPrice - buyingPrice);
  }

  // return the max profit
  return maximumProfit;
};

// Time Complexity: O(n)
// Space Complexity: O(1)