maxStockProfit.js

/*-----------------------------------------------------------------------------
1.apply what we learn to find to minimun and maximum stock price
2.remember that the sell price is later than the buy price

NOTE: The first function I wrote was too simple to cover the situations

the reference used at the second function is from UdemyCourse: LearningAlgorithmsInJavascriptFromScratch
-----------------------------------------------------------------------------*/

function maxStockProfit(priceArr) {
  var priceArrCopied = Array.prototype.slice.call(priceArr);
  var priceSorted = priceArr.sort((a, b) => {
    return a - b;
  });
  var highOrder = priceArrCopied.indexOf(priceSorted[priceSorted.length - 1]);
  var lowOrder = priceArrCopied.indexOf(priceSorted[0]);

  if (lowOrder > highOrder) return -1;
  else return priceSorted[priceSorted.length - 1] - priceSorted[0];
}
maxStockProfit([10, 18, 4, 5, 9, 6, 16, 12]);

maxStockProfitOfficial.js

function maxStockProfit2(priceArr) {
  var maxProfit = -1,
    temProfit,
    sellPrice = 0,
    buyPrice = 0,
    r,
    keepChanging = true;

  for (r = 0; r < priceArr.length; r++) {
    if (keepChanging) {
      buyPrice = priceArr[r];
    }
    sellPrice = priceArr[r + 1];

    if (sellPrice < buyPrice) {
      keepChanging = true;
    } else {
      temProfit = sellPrice - buyPrice;
      if (temProfit > maxProfit) {
        maxProfit = temProfit;
      }
      keepChanging = false;
    }
  }
  return maxProfit;
}
maxStockProfit2([10, 18, 4, 5, 9, 6, 16, 12]);