Buy and Sell Stocks All Variants in DSA C - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main goal in the 'Buy and Sell Stocks' problem?

To find the maximum profit by choosing the best days to buy and sell stocks given their prices over time.

beginner

In the single transaction variant, what is the key idea to find maximum profit?

Track the minimum price seen so far and calculate the profit if sold today; update max profit accordingly.

intermediate

How does the multiple transactions variant differ from the single transaction variant?

You can buy and sell multiple times, so the goal is to sum all positive price differences between consecutive days.

intermediate

What constraint does the 'at most two transactions' variant add?

You can complete at most two buy-sell transactions to maximize profit, requiring tracking profits from left and right passes.

advanced

Why is dynamic programming useful in the 'Buy and Sell Stocks with cooldown' variant?

Because you must consider cooldown days after selling, DP helps track states like holding, sold, and cooldown to maximize profit.

In the single transaction stock problem, what do you track to find max profit?

A Maximum price so far only

B Minimum price so far and max profit

C Sum of all prices

D Number of transactions

Tracking the minimum price so far allows calculating potential profit if sold today, updating max profit.

For multiple transactions allowed, how do you calculate max profit?

A Sum all positive differences between consecutive days

B Buy on first day, sell on last day

C Only one transaction allowed

D Ignore price drops

Adding all positive price differences captures profit from every profitable buy-sell pair.

What is the main challenge in the 'at most two transactions' variant?

A No transactions allowed

B Only one transaction allowed

C Tracking profits from two separate transactions efficiently

D Ignoring price changes

You must find two non-overlapping transactions that maximize combined profit.

In the cooldown variant, what happens after selling a stock?

A You must wait one day before buying again

B You can buy immediately

C You cannot buy ever again

D You must sell again immediately

Cooldown means you cannot buy on the day immediately after selling.

Which approach is best for solving complex variants like cooldown or transaction limits?

A Greedy without tracking states

B Brute Force

C Sorting prices

D Dynamic Programming

Dynamic Programming efficiently tracks states and decisions to maximize profit under constraints.

Explain how to find maximum profit with only one buy and one sell allowed.

Think about the lowest price before the current day.

Describe the difference between multiple transactions allowed and cooldown variants.

Cooldown adds waiting days after selling.