Leetcode 123. Best Time to Buy and Sell Stock III  Summary and Q&A
TL;DR
Learn how to calculate maximum profit from at most two stock transactions.
Key Insights
 ⛔ Maximizing profit from stock trading requires strategic planning of buying and selling, especially with transaction limits.
 👣 Keeping track of minimum prices and maximum profits for both transactions is essential for deriving an optimal solution.
 ⚾ An effective price for the second transaction is calculated by adjusting the stock price based on the profit made from the first transaction.
 💐 The algorithm benefits from a clear definition of variables, making it easier to understand the flow and logic of the solution.
 The example given demonstrates practical applications, ensuring viewers grasp the concepts clearly.
 👾 Constant space complexity is a significant advantage in situations with large datasets.
 🍂 The algorithm effectively handles various scenarios, including cases where no profit can be made due to falling prices.
Transcript
hey there everyone welcome back to lead coding in this video we will be solving the third part of the problem buy and sell stock we have already covered the part 1 and part 2 and i think by the time you will be watching this video part 4 will also be covered now we are going to look at part three let us read the problem statement so we have an arra... Read More
Questions & Answers
Q: What problem does the video address regarding stock trading?
The video addresses the challenge of maximizing stock trading profits by allowing at most two transactions. Unlike previous parts, which had different constraints on transactions, this segment focuses on optimizing profits based on these new limits using a specific algorithm.
Q: How does the approach to the second transaction differ from the first?
The second transaction’s approach incorporates the profit from the first transaction to determine an effective buying price for the stock. This means adjusting the current stock price downwards by the profit already gained, allowing the optimization of the second profit based on this new effective price.
Q: What variables are used to store prices and profits in the algorithm?
The algorithm employs four key variables: minimum price for the first transaction, profit from the first transaction, minimum price for the second transaction, and profit from the second transaction. This structure allows the algorithm to keep track of all relevant prices and profits during the calculations.
Q: What are the expected complexities of the algorithm?
The algorithm is characterized by constant space complexity because it only utilizes four variables, regardless of the input size. The time complexity, however, is linear (O(n)), meaning it efficiently processes each price in the array in a single pass.
Summary & Key Takeaways

The video focuses on solving the problem of maximizing stock trading profits with the constraint of two transactions, as part of a series on the topic.

It explains the logic of keeping track of the minimum stock prices and profits for both transactions while providing examples to illustrate how to implement the solution.

The algorithm's complexity is discussed, highlighting constant space usage and linear time complexity, making it efficient for large datasets.