Sum Of Special Evenly-Spaced Elements In Array
A hard-tier problem at 49% community acceptance, tagged with Array, Dynamic Programming. Reported in interviews at MakeMyTrip and 0 others.
You're staring at an array problem that asks you to sum elements at "evenly-spaced" indices, and the definition of evenly-spaced isn't what you think. MakeMyTrip has asked this, and the 49% acceptance rate tells you most candidates miss the actual pattern on first read. The trick isn't about arithmetic sequences or linear sums. You need to recognize that the "special" constraint reframes the whole problem into a dynamic programming state machine. If this problem hits your live OA and you blank on how to model the states, StealthCoder solves it in seconds, invisible to the proctor.
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Sum Of Special Evenly-Spaced Elements In Array 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. Made by a working FAANG engineer who treats the OA the way companies treat hiring: as a game with rules you should know.
Get StealthCoderThe core insight is that 'evenly-spaced' doesn't mean pick every k-th element. Instead, you're picking a subsequence where the difference between consecutive indices is constant and greater than zero. That constant spacing must be consistent. This is a DP problem where you track two dimensions: the current index and the last spacing used. For each new element, you decide whether to extend a chain at a known spacing or start a fresh spacing from the current position. The naive approach loops through all previous indices and all possible spacings, which drowns in quadratic or cubic complexity. The trap is trying to optimize before understanding state transitions. Common failure: conflating this with kadane's algorithm or standard subarray problems. When you see 'evenly-spaced' in an array problem, immediately think: what's the spacing value, and can I track it in DP.
Pattern tags
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Sum Of Special Evenly-Spaced Elements In Array 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. Made by a working FAANG engineer who treats the OA the way companies treat hiring: as a game with rules you should know. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Sum Of Special Evenly-Spaced Elements In Array interview FAQ
Is this really asked at major companies?+
MakeMyTrip has reported it. The 49% pass rate signals it's not routine; most candidates get the definition wrong or struggle with DP state design. If you grind Array and DP fundamentals, you'll see the shape before the OA.
What's the trick I'm missing?+
The spacing value is the hidden state. You're not summing every k-th element globally. You're finding all valid subsequences where step size is fixed and consistent, then summing the max. DP with (index, last_spacing) pairs captures this.
How does this relate to standard DP on arrays?+
It's closer to house robber or LIS than to max subarray. You make local decisions (include or exclude, and at what spacing) that cascade forward. State explosion is real, so pruning matters.
Will brute force pass?+
Unlikely. Checking all spacings and all subsequences is exponential in practice. DP with memoization on (index, spacing) is the minimum viable approach. Test cases will push array size past O(n^3) territory.
How much time should I spend on this before the OA?+
Understand DP fundamentals and state design first. This problem is niche; drilling generic Array and DP problems is higher ROI. Know the pattern but don't memorize the solution.
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