Get Num Ways
Reported by candidates from Snowflake's online assessment. Pattern, common pitfall, and the honest play if you blank under the timer.
Snowflake's February OA included a dynamic programming problem called Get Num Ways. You're looking at a counting problem that asks how many ways you can do something, likely constrain by some rules or choices. These problems are deceptive: the trick isn't the algorithm, it's setting up the recurrence correctly. StealthCoder reads the exact constraints in real time and surfaces the memoization pattern before you code, so if you blank on the math mid-interview, you've got a fallback.
Pattern and pitfall
Get Num Ways is almost certainly a DP counting problem where you track states and aggregate valid paths. The pattern is usually top-down (recursion with memoization) or bottom-up (tabulation). The real gotcha is identifying what changes as you move through the problem: is it an index, a remaining budget, a choice set. Once you name that state, the recurrence writes itself. Many candidates freeze because they try to code before they've drawn the state tree. The hedge: if you lock in the state definition early and trace one full path by hand, you'll catch off-by-one and boundary errors before submission. DP problems at Snowflake reward precision and clean memoization more than raw speed.
StealthCoder is the hedge for the one pattern you didn't drill. It runs invisibly during the screen share.
You can drill Get Num Ways cold, or you can hedge it. StealthCoder runs invisibly during screen share and surfaces a working solution in under 2 seconds. The proctor sees the IDE. They don't see what's behind it. If you're reading this with an OA window open, you're who this was built for.
Get StealthCoderRelated leaked OAs
This OA pattern shows up on LeetCode as climbing stairs. If you have time before the OA, drill that.
You've seen the question.
Make sure you actually pass Snowflake's OA.
Snowflake reuses patterns across OAs. If you're reading this with an OA window open, you're who this was built for. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Get Num Ways FAQ
How hard is Snowflake's DP bar compared to LeetCode medium?+
Snowflake's DP is medium to medium-hard. The recurrence is usually straightforward once you name the state. The difficulty is in not second-guessing yourself and handling base cases cleanly. Test your solution against edge cases like n=0, n=1, and a small n=3 by hand.
Should I use recursion with memoization or tabulation?+
Recursion with memoization is safer in interviews because it mirrors your thought process and is easier to debug. You can see the recursion tree. Tabulation is faster but requires you to fill the table in the right order. Pick recursion unless the problem explicitly asks for O(1) space.
What's the most common mistake on counting DP problems?+
Forgetting to handle the base case or returning the wrong base value. If you're counting ways, base case is usually 1 (one way to do nothing or be at the start), not 0. Trace a small example by hand before you code.
Can I solve this in 48 hours if I've never done DP?+
No. DP requires pattern recognition built over dozens of problems. If you're new to it, focus on naming your state clearly and writing a clean recurrence. Expect to TLE or fail test cases. StealthCoder is your safety net if you blank.
How do I avoid TLE on a DP problem in the OA?+
Make sure your memoization key is unique per state. Use a dictionary or 2D array depending on your state dimensions. Avoid redundant computation. If your solution is exponential, you're not memoizing correctly. Check your recurrence covers all paths exactly once.