If the wiggle subsequence problem is modified so that the absolute difference between consecutive elements must alternate in sign AND be at least a threshold k (> 0), how should the optimal algorithm be adapted?
hard🔁 Follow-up Q10 of Q15
Greedy Algorithms - Wiggle Subsequence
If the wiggle subsequence problem is modified so that the absolute difference between consecutive elements must alternate in sign AND be at least a threshold k (> 0), how should the optimal algorithm be adapted?
AUse the original greedy algorithm without changes since threshold doesn't affect logic
BModify the greedy approach to only update counts when |diff| ≥ k and sign alternates
CSort the array first to ensure differences meet the threshold
DApply dynamic programming with O(n^3) complexity to handle threshold
Step-by-Step Solution
Solution:
Step 1: Understand the new constraint
Differences must alternate in sign and have absolute value ≥ k.
Step 2: Adapt greedy algorithm
Update counts only when the difference's absolute value meets or exceeds k and sign alternates.
Step 3: Reject other options
Sorting breaks subsequence order; DP with O(n^3) is unnecessary overhead.
Final Answer:
Option B -> Option B
Quick Check:
Threshold filters differences before counting [OK]
Quick Trick:Add threshold check to greedy sign alternation logic [OK]
Common Mistakes:
MISTAKES
Ignoring threshold and using original algorithm
Sorting array which breaks subsequence order
Overcomplicating with high-complexity DP
Trap Explanation:
PITFALL
Ignoring threshold seems simpler but yields incorrect results
Interviewer Note:
CONTEXT
Tests ability to adapt algorithms to additional constraints
Master "Wiggle Subsequence" in Greedy Algorithms
3 interactive learning modes - each teaches the same concept differently
