Identifying the Problem

We want to figure out the greatest possible profit from buying and selling a stock. The sequence of stock prices is represented by an array, and each element indicates the price on a particular day.

Starting with Basic Understanding

Initially, we might think that finding the maximum and minimum prices would suffice. However, the requirement that we must buy before selling adds a twist.

Realizing the Complexity

We realize that the order of prices matters, so the minimum price must occur before the maximum price.

Understanding the Challenge

The problem isn't as straightforward as finding the largest and smallest elements. Here's why:

• Buying before Selling Rule: We must buy before selling, so order matters. Simply finding max and min values is not enough; we need to ensure that the min value comes before the max.

Crafting the Solution

Given the constraint of buying before selling, we can sketch out a plan as follows:

1. Iterate Through Days: We'll iterate through each element (day) in the array.

2. Compare with Future Days: At each day, we'll check the difference between the price of that day and only the prices on days after it.

3. Nested Loops: This can be achieved with a simple nested for-loop.

   • The first loop goes through all the days.
   • At each day, a second loop (starting from j = i + 1) compares the price of the day to only the prices on subsequent days.

4. Maximize Profit: During the iteration, we'll keep track of the minimum price so far and the maximum profit obtainable. The difference between the current price and the minimum price will help us find the maximum profit.

Why This Approach Works

• Adheres to the Rule: By comparing a price only with prices on subsequent days, we ensure that buying occurs before selling.
• Efficiency: This approach leads to a solution within the given constraints.

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function stockOptimizer(prices) {

  let maxDiff = 0;

  for (let i = 0; i < prices.length; i++) {

    for (let j = i + 1; j < prices.length; j++) {

      let newDiff = prices[j] - prices[i];

​

      if (newDiff > maxDiff) {

        maxDiff = newDiff;

      }

    }

  }

​

  return maxDiff;

}

​

console.log(stockOptimizer([2, 5, 15, 9]));