Done Competitive-Coding-10

[samikshm]

No description provided.

[super30admin]

The student has submitted two solutions for what appear to be two separate coding problems:

Solution 1: buy_and_sell_stock_2.java (Best Time to Buy and Sell Stock II)

Correctness: The solution correctly implements the greedy approach for the "Best Time to Buy and Sell Stock II" problem. By capturing profit from every upward price movement (prices[i] > prices[i-1]), the algorithm correctly accumulates the maximum profit, which is mathematically equivalent to performing complete transactions during any upward trend.

Time Complexity: O(n) - The solution traverses the array once, examining each consecutive pair of prices.

Space Complexity: O(1) - Only a constant amount of extra space is used (the profit variable and loop counter).

Code Quality: The code is clean, well-structured, and includes helpful comments explaining the approach. Variable names are descriptive, and the logic is straightforward to follow. The three-sentence explanation at the top effectively summarizes the greedy strategy.

Efficiency: The solution is optimal for this problem. The greedy approach of capturing all positive differences is the standard O(n) solution and cannot be improved upon in terms of time complexity.

Edge Cases Considered: The solution handles the edge case of a non-increasing price array (where profit remains 0) correctly, as no positive differences would be added.

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Solution 2: peeking_iterator.java (Peeking Iterator)

Correctness: The solution correctly implements the Iterator pattern with peek functionality. The prefetch mechanism (storing the next element in advance) allows peek() to return the next value without advancing the iterator. The next() method properly returns the prefetched value and prefetches the subsequent element. The hasNext() method correctly reflects whether a prefetched value exists.

Time Complexity: O(1) for all operations (peek(), next(), hasNext()) - Each operation performs constant-time work.

Space Complexity: O(1) - Only a fixed number of instance variables are used regardless of input size.

Code Quality: The code is well-structured with clear separation of concerns. The advance() helper method encapsulates the prefetch logic, making the code more readable. The use of Boolean wrapper type for hasPeeked is appropriate since it needs to represent a three-state condition (no peek yet, peeked value exists, no more elements). However, the variable naming could be slightly improved - hasPeeked is slightly misleading since it indicates whether a valid next value is available, not whether peek() has been called.

Efficiency: The solution is efficient. The prefetch approach ensures that each element is read from the underlying iterator exactly once, which is optimal.

Edge Cases Considered: The solution handles the edge case of an empty iterator correctly - advance() sets nextVal to null and hasPeeked to false, so hasNext() returns false and peek()/next() behave appropriately.

Minor Suggestions:

1. In the PeekingIterator, consider renaming hasPeeked to hasNextVal or nextAvailable for clarity, as the current name could be misinterpreted.
2. The peek() method could benefit from a null check to prevent returning null when there are no more elements, though this is typically the caller's responsibility per the problem specification.