Good afternoon! Here's our prompt for today.

This is a classic technical interview question that I've seen a number of times in real life interviews. Let's say you're given an array of stock prices, with each element being an integer that represents a price in dollars.

1[ 10, 7, 6, 2, 9, 4 ]

Each index of the array represents a single day, and the the element at that index is the stock price for that given day. This means that the array below represents:

1let prices = [10, 7, 6, 2, 9, 4];
2// Day 0 - a price of `$10`
3// Day 1 - `$7`
4// Day 2 - `$6` (and so on...)

Given the ability to only buy once and sell once, our goal is to maximize the amount of profit (selling price - purchase price) that we can attain and return that value. Note the only caveat is that that we cannot sell a stock before we buy it, which is important in identifying a solution.

Can you write a stock optimizer method called stockOptimizer? See the following examples for further clarification:

1stockOptimizer([10, 7, 6, 2, 9, 4]);
2// 7

For the above example, the max profit is made when we buy on day/index 3 (when the price is 2) and sell on day/index 4 (when the price is 9). 9 - 2 gives us 7, which is returned by the function. Let's do another example.

1stockOptimizer([9, 8, 6, 5, 3]);
2// 0

From a quick glance, it seems like there's enough price differences to generate a profit. However, notice that the price drops every day, and thus we can't have a profit since we're required to buy before selling.

Constraints

• Length of the given array <= 100000
• The array will always consist of non zero integer (including 0)
• The maximum price would be <= 2147483647
• Expected time complexity : O(n)
• Expected space complexity : O(1)
• The array would always contain more than 1 element

Try to solve this here or in Interactive Mode.

How do I practice this challenge?

xxxxxxxxxx

    'PASSED: ' + 'stockOptimizer([14,3,16,8,9,7,8,18,15,10,9]) should return 15'

var assert = require('assert');

​

function stockOptimizer(prices) {

  // Fill in this method

  return prices;

}

​

try {

  assert.deepEqual(stockOptimizer([14, 20, 9]), 6);

​

  console.log('PASSED: ' + 'stockOptimizer([14,20,9]) should return 6');

} catch (err) {

  console.log(err);

}

​

try {

  assert.deepEqual(stockOptimizer([5, 20, 15, 13, 3, 15, 5, 10]), 15);

​

  console.log(

    'PASSED: ' + 'stockOptimizer([5,20,15,13,3,15,5,10]) should return 15'

  );

} catch (err) {

  console.log(err);

}

​

try {

  assert.deepEqual(stockOptimizer([1, 6, 11, 2]), 10);

​

  console.log('PASSED: ' + 'stockOptimizer([1,6,11,2]) should return 10');

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Here's how we would solve this problem...

How do I use this guide?