Zigzag Conversion
A medium-tier problem at 52% community acceptance, tagged with String. Reported in interviews at ConsultAdd and 23 others.
Zigzag Conversion is a medium-difficulty string problem that appears in assessments across PayPal, ServiceNow, Zoho, and 21 other companies. It's deceptively simple to state: arrange a string in a zigzag pattern across a given number of rows, then read it off line by line. The trap is that candidates often overthink the geometry and waste time building explicit 2D arrays. In reality, the pattern is directional. You're moving down, then up, then down again. Once you map which row each character lands in without storing the grid itself, you're done. If you freeze on the pattern during your live assessment, StealthCoder runs invisibly and delivers the solution in seconds.
Companies that ask "Zigzag Conversion"
Zigzag Conversion 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 an engineer at a top-10 tech company who can solve these problems cold but didn't want to trust himself in a 90-minute screen share.
Get StealthCoderThe key insight is direction tracking. Start at row 0, move down to row numRows-1, then bounce back up to row 0, and repeat. Instead of building a 2D matrix, use numRows separate lists or strings to collect characters by row number. As you iterate through the input string, increment or decrement the current row index based on whether you're moving down or up. When you hit the top or bottom boundary, flip direction. The tricky part isn't the zigzag itself, it's resisting the urge to materialize the grid and instead track only the row index and direction. Many candidates write nested loops or indexing math that's fragile. A direction flag and boundary checks handle it cleanly. With 51.6% acceptance rate, half the candidates are either over-engineering or miscounting boundary transitions. This is exactly where StealthCoder is the hedge: you walk in, the pattern clicks, invisible safety net in place.
Pattern tags
You know the problem.
Make sure you actually pass it.
Zigzag Conversion recycles across companies for a reason. It's medium-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 an engineer at a top-10 tech company who can solve these problems cold but didn't want to trust himself in a 90-minute screen share. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Zigzag Conversion interview FAQ
Is Zigzag Conversion actually asked at major companies?+
Yes, it's been reported at PayPal, ServiceNow, Zoho, and 21 others across finance, SaaS, and consumer tech. It's a reliable medium-difficulty warm-up or follow-up question, not a flagship hard problem. Acceptance rate is roughly 51.6%, so it's a decent filter for distinguishing who can handle string manipulation without overcomplicating.
What's the main trick everyone misses?+
Building an actual 2D array or matrix. The zigzag pattern is just row indices moving up and down. Use a direction flag and a single row counter. As you iterate the string, append each character to the corresponding row list, flip direction at boundaries, move on. No grid needed.
How do I avoid off-by-one errors on row boundaries?+
Flip direction when row == 0 or row == numRows - 1. Most mistakes happen because candidates check row < 0 or row >= numRows, but you want to flip before the invalid access. Test with numRows = 2 and numRows = 3 to verify your boundary logic holds.
What languages is this typically asked in?+
It's language-agnostic, but Python and Java dominate reports. The core logic is the same everywhere: iterate, track row and direction, bucket by row, concatenate. No language quirk changes the pattern recognition.
If I blank on this during the real assessment, how much time does it cost?+
If you're unprepared and don't see the direction-flip pattern, you could lose 20-40 minutes flailing on a 2D approach. That's why StealthCoder exists: you hit the problem cold, it surfaces a clean solution in seconds, and you move on without panic.
Want the actual problem statement? View "Zigzag Conversion" on LeetCode →