// Suppose we could access yesterday's stock prices as an array, where: // The indices are the time in minutes past trade opening time, which was 9:30am local time. The values are the price in dollars of Apple stock at that time. // So if the stock cost $500 at 10:30am, stockPricesYesterday[60] = 500. // Write an efficient function that takes st…

yesterday_stock.js

// Suppose we could access yesterday's stock prices as an array, where:
// The indices are the time in minutes past trade opening time, which was 9:30am local time. The values are the price in dollars of Apple stock at that time. 
// So if the stock cost $500 at 10:30am, stockPricesYesterday[60] = 500.
// Write an efficient function that takes stockPricesYesterday and returns the best profit I could have made from 1 purchase and 1 sale of 1 Apple stock yesterday.
// The expected format is:
// 6 (buying for $5 and selling for $11)

function utcTime(date) {
  try {
    if (date instanceof Date) {
      var utc = date.getTime() - (date.getTimezoneOffset() * 60000);
      date.setTime(utc);
      return date;
    } else {
      throw new Error('"date" is not an instance of Date');
    }
  } catch (error) {
    console.error(error);
  }
}

function getOpeningDateTime(date) {
  try {
    if (date instanceof Date) {
      date.setHours(9,30,0,0);
      return utcTime(date);
    } else {
      throw new Error('"date" is not an instance of Date');
    }
  } catch (error) {
    console.error(error);
  }
}

function getDateYesterday() {
  let yesterday = new Date(Date.now() - 86400000);
  return yesterday;
}

function removeIndex(indexToRemove, arr) {
  return arr.filter(function(price, index) {
    return indexToRemove !== index
  });
}

function getMinPrice(stockPricesYesterday) {
  return stockPricesYesterday.reduce(function(a, b) {
    return Math.min(a, b);
  });
}

function getMaxPrice(stockPricesYesterday) {
  return stockPricesYesterday.reduce(function(a, b) {
    return Math.max(a, b);
  });
}

function getMaxProfit(stockPricesYesterday) {
  if (stockPricesYesterday.length === 0) return;

  const yesterday = getDateYesterday();
  const openingDateTime = getOpeningDateTime(yesterday);

  const minPrice = getMinPrice(stockPricesYesterday);
  const maxPrice = getMaxPrice(stockPricesYesterday);

  const minPriceIndex = stockPricesYesterday.indexOf(minPrice);
  const maxPriceIndex = stockPricesYesterday.indexOf(maxPrice);

  if (maxPriceIndex < minPriceIndex) {
    const newStockPricesYesterday = removeIndex(minPriceIndex, stockPricesYesterday);
    return getMaxProfit(newStockPricesYesterday);
  }

  const profit = maxPrice - minPrice;

  return `${profit} (buying for $${minPrice} and selling for $${maxPrice})`;
}

var stockPricesYesterday = [10, 7, 5, 8, 11, 9, 2];

console.log(getMaxProfit(stockPricesYesterday));
// returns 6 (buying for $5 and selling for $11)