Number of Ways to Separate Numbers
A hard-tier problem at 21% community acceptance, tagged with String, Dynamic Programming, Suffix Array. Reported in interviews at Walmart Labs and 0 others.
You're given a string of digits and need to count how many ways you can insert plus signs to create a valid arithmetic expression. Walmart Labs uses this one. The acceptance rate sits at 21%, which means most candidates either miss the DP state or tank on parsing valid numbers. The trick is recognizing that you're not actually evaluating expressions, you're counting partitions where each segment is a valid number (no leading zeros). If you hit this live and blank on the state transition, StealthCoder will surface the working solution in seconds, invisible to the proctor.
Companies that ask "Number of Ways to Separate Numbers"
Number of Ways to Separate Numbers is the kind of problem that decides whether you pass. StealthCoder reads the problem on screen and surfaces a working solution in under 2 seconds. Invisible to screen share. The proctor sees nothing. Built by a senior engineer who knows the OA is theater. This is the script.
Get StealthCoderThe core problem is a DP counting question disguised as math. You iterate through the string, and at each position you decide whether to place a plus sign or continue the current number. The state is your position in the string and the count of valid ways to partition everything up to that point. The real gotcha is the leading-zero rule: "0" is valid, but "01" or "001" aren't. Most candidates either skip this validation or implement it wrong, which silently breaks test cases. Another trap is confusing this with subset problems or trying to actually evaluate expressions. You're purely counting valid split points. The complexity is manageable (O(n^2) or O(n^3) depending on your number-validation approach), but the implementation details are fiddly. When you're live in the assessment and the brute-force backtracking approach times out on large inputs, that's when the DP structure matters. StealthCoder handles the substring-to-integer conversion and overlap cases so you don't lose points to off-by-one errors.
Pattern tags
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Number of Ways to Separate Numbers recycles across companies for a reason. It's hard-tier, and most candidates blank under the timer. StealthCoder is the hedge: an AI overlay invisible during screen share. It reads the problem and surfaces a working solution in under 2 seconds. Built by a senior engineer who knows the OA is theater. This is the script. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Number of Ways to Separate Numbers interview FAQ
Is this really asked at Walmart Labs interviews?+
Yes, confirmed in their hiring loop. It's a solid medium-to-hard DP problem that tests whether you can set up state cleanly and handle string parsing edge cases. Not a trick question, but definitely not trivial. Most candidates see it once in their prep and never forget it.
Why is the acceptance rate so low?+
The leading-zero constraint trips up most people. You have to explicitly reject any number that starts with zero (except '0' itself). Combined with a slightly non-obvious DP transition, candidates either implement a slow solution that times out or introduce subtle bugs in validation. The 21% rate reflects those two failure modes.
What's the difference between this and just checking all partitions?+
Brute force (try all 2^n partitions) is exponential and won't pass large inputs. DP memoizes the count at each position, bringing it down to polynomial time. The trick is storing only the position index and the count, not the actual partitions themselves.
Do I need Suffix Array for this problem?+
Suffix Array is listed as a topic, but most accepted solutions use only String and Dynamic Programming. Suffix Array approaches exist for certain optimizations or alternative structures, but they're not required. Standard DP solutions pass comfortably.
How much time should I spend on this in a real OA?+
If you recognize the DP structure immediately, 20-30 minutes should get you to a working solution. If you're struggling with the state or the leading-zero logic after 15 minutes, you're likely overthinking it. That's when a tool like StealthCoder becomes your safety net.
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