Leetcode 121. Best Time to Buy and Sell Stock  Summary and Q&A
TL;DR
This video discusses an algorithm to maximize stock trading profit with one transaction.
Key Insights
 ❓ Understanding the LeetCode problem "Best Time to Buy and Sell Stock" is crucial for mastering algorithmic trading concepts.
 🥳 The problem requires a strategy for selecting optimal buying and selling days to maximize profit.
 🌥️ An O(n^2) solution is intuitive but inefficient for large datasets.
 🔁 The optimized algorithm reduces complexity significantly by utilizing a single loop approach.
 👣 The algorithm emphasizes the importance of keeping track of the minimum stock price encountered during iterations.
 😘 Profit calculations focus on the difference between selling prices and the lowest possible buy price seen until that point.
 💦 Viewers can benefit from visual examples to grasp the algorithm's working effectively.
Transcript
hey there everyone welcome back to lead coding in this video we are going to cover a very famous interview problem called best time to buy and sell stock on lead code there are four part of the same problem currently there are four parts in future if they are going to add more we will be providing the solution to that as well but as of now we will ... Read More
Questions & Answers
Q: What is the main problem addressed in the video?
The video addresses a popular algorithm problem from LeetCode, known as "Best Time to Buy and Sell Stock," which involves determining the maximum profit one can achieve from buying and selling a stock, limited to one transaction.
Q: How does the algorithm initially proposed work?
The initially proposed algorithm has a time complexity of O(n^2), where it examines each possible buysell pair by iterating through the days. For each day, it calculates the profit from buying on that day and selling on each subsequent day, looking for the maximum profit.
Q: What optimization does the video suggest for the algorithm?
The video suggests an optimization by tracking the minimum price seen so far and calculating the maximum profit in a single pass. This reduces the time complexity to O(n) by only needing to traverse the price list once, thereby improving efficiency significantly.
Q: How is profit calculated in the optimized approach?
In the optimized approach, for each day, the algorithm updates the minimum price encountered. The profit for selling on that day is calculated by subtracting this minimum price from the current day's price. The global maximum profit is updated if the calculated profit exceeds the previously recorded maximum.
Q: What are the time and space complexities of the final solution?
The final solution has a time complexity of O(n), since it requires a single pass through the price list. The space complexity is constant O(1) as it uses a fixed amount of additional space (for variables) regardless of the input size.
Q: Can the algorithm handle scenarios with no profit opportunity?
Yes, the algorithm can handle scenarios where no profitable transaction is possible. In such cases, the maximum profit will remain at its initialized value of zero if there is never a situation where the current price exceeds the minimum price seen so far.
Q: Where can viewers find more resources on this problem?
Viewers are encouraged to check the description of the video for links to all parts of the problem, as well as additional related content on the channel to enhance their understanding of stock trading algorithms.
Summary & Key Takeaways

The video focuses on a wellknown algorithmic problem from LeetCode regarding stock trading, where the goal is to find the maximum profit from a single buy and sell transaction.

It presents the problem statement and illustrates the methodology using a practical example of stock prices over six days, emphasizing the importance of selecting the optimal days to buy and sell.

By analyzing the problem, the video proposes an efficient O(n) solution to find the maximum profit by tracking the minimum price and calculating potential profits as prices fluctuate over the days.