Disappeared Numbers (Problem31.java)

Your solution is well-implemented and efficient. You have correctly used the in-place marking technique to solve the problem without extra space and in linear time. The code is clean and well-commented.

One thing to note: although your solution is correct, it modifies the input array. This might be acceptable in many contexts, but if the input array needs to be preserved, you would need to restore it. However, the problem does not specify whether the input can be modified, so it's generally acceptable.

Also, consider adding a comment explaining the approach briefly for better clarity. For example:
// Mark indices as negative to indicate presence of the number
// Then, indices with positive values correspond to missing numbers

Overall, great job!

VERDICT: PASS

max and min (Problem32.java)

Your solution is excellent and matches the optimal approach. You have correctly handled both even and odd-length arrays by initializing min and max appropriately. The use of pairs minimizes the number of comparisons, which meets the problem requirement. The code is clean and well-commented. One minor suggestion: consider adding a check for an empty input array, though the problem states "an array of numbers" so it might be assumed non-empty. However, in production code, handling edge cases like empty arrays is good practice. Overall, great job!

VERDICT: PASS

Life Game (Problem33.java)

Your solution is excellent and matches the reference solution closely. Here are some strengths and minor suggestions:

Strengths:

• You correctly used the in-place technique with intermediate states (2 for "alive to dead" and 3 for "dead to alive") to handle simultaneous updates.
• The getCount method efficiently checks all eight neighbors and correctly considers intermediate states (1 and 2 as alive, since 2 represents a currently alive cell that will become dead in the next state).
• The code is clean, well-organized, and includes comments.

Areas for improvement:

• The time complexity comment in your code says "O(n)" but it should be "O(m*n)" since the grid has m rows and n columns. This is a minor oversight.
• Consider adding more detailed comments in the getCount method to explain why you are counting cells with value 1 or 2 as alive (because 2 represents a live cell that will die in the next state, but for the current state it is still alive).
• The problem constraints are small (m, n <= 25), so the solution is efficient. However, for larger boards (as mentioned in the follow-up), you might consider how to handle infinite boards. This is beyond the scope of the problem, but it's good to think about.

Overall, your solution is correct and efficient. Keep up the good work!

VERDICT: PASS