Greedy Algorithms - Best Time to Buy and Sell Stock II
What is the time complexity of the peak-valley approach for the Best Time to Buy and Sell Stock II problem, and why might some candidates incorrectly think it is higher?
What is the time complexity of the peak-valley approach for the Best Time to Buy and Sell Stock II problem, and why might some candidates incorrectly think it is higher?
medium🪤 Complexity Trap Q13 of Q15
Step-by-Step Solution
Solution:
Step 1: Identify loop behavior
Though there are nested while loops, the index i only moves forward and never revisits elements.Step 2: Conclude time complexity
Each element is processed at most twice, so total time is linear O(n).Final Answer:
Option D -> Option DQuick Check:
Index i increments monotonically through array [OK]
Quick Trick: Index i only moves forward, no repeated visits [OK]
Common Mistakes:
MISTAKES- Assuming nested loops multiply to O(n^2)
- Confusing space complexity with time complexity
- Thinking sorting is involved
Trap Explanation:
PITFALL- Nested loops suggest O(n^2) but careful index movement shows linear time.
Interviewer Note:
CONTEXT- Tests understanding of loop invariants and complexity beyond superficial code structure.
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