1. Next Greater Element (classic) 2. Daily Temperatures (distance tracking) 3. Largest Rectangle in Histogram (area calculation with left/right bounds). Once you master monotonic stacks, all three problems use the exact same 15-line while-loop structure.

Stuck at Specialist for 4 months. I can consistently solve Div 2 A and B in 20 minutes, but C always trips me up with either Time Limit Exceeded (TLE) or subtle math proofs. What was the turning point that pushed you into Candidate Master?

Problem C was all about parity observation rather than greedy simulation. If you noticed that odd and even indices could be sorted independently, the solution reduced to O(N log N). Problem D had tricky corner cases with zero-weight edges. How did everyone's rating delta go?

Shared my C++ snippet for preprocessing 2^k ancestor tables `up[node][k]` in O(N log N) time and querying Lowest Common Ancestor (LCA) in O(log N). Much easier to implement under contest pressure than Heavy-Light Decomposition unless path updates are needed.