Debugger Breakpoint Actions
Reported by candidates from TikTok's online assessment. Pattern, common pitfall, and the honest play if you blank under the timer.
The mistake that sinks a first attempt on this TikTok OA, reported in August 2026, is treating "continue" as "jump to the next breakpoint in the array" instead of "first breakpoint strictly after the current line." Those aren't the same thing once "next" moves you past breakpoints. The problem is simulation with a sorted array, nothing fancy. You track one pointer for the current line and handle two action types. It looks trivial, and that's exactly why people rush it and lose points on the examples. If you blank on the lookup logic during the live assessment, StealthCoder runs invisibly as a safety net.
The problem
A debugger starts on line 1 of a code snippet whose final line is codeLength. The sorted array breakpoints contains the unique line numbers that have breakpoints. Process the strings in actions in order: "next" moves the debugger forward by exactly one line. "continue" moves the debugger to the first breakpoint strictly after its current line. Every action is valid: "next" is never used on the final line, and a later breakpoint always exists for "continue". Return the line on which the debugger stops after every action has been processed. Function debuggerFinalLine(codeLength: int, breakpoints: int[], actions: String[]) → int Examples Example 1 codeLength = 55 breakpoints = [2,5,21,44] actions = ["next","next","continue","next","next"] return = 7 The two "next" actions move from line 1 to line 3. The next breakpoint after line 3 is line 5, and the final two actions move to line 7. Example 2 codeLength = 10 breakpoints = [4,8] actions = ["continue","next","continue"] return = 8 The debugger continues to line 4, advances to line 5, and then continues to line 8. Example 3 codeLength = 6 breakpoints = [2,4,6] actions = ["next","continue","next"] return = 5 The debugger moves to line 2, continues to the next breakpoint on line 4, and advances once to line 5. Constraints codeLength >= 1 breakpoints is sorted in strictly increasing order. 1 <= breakpoints[i] <= codeLength Every action is either "next" or "continue". A "next" action is never performed on line codeLength. For every "continue" action, a breakpoint exists strictly after the current line.
Reported by candidates. Source: FastPrep
Pattern and pitfall
The core is simulation. Keep a variable line starting at 1. For "next", add one. For "continue", find the smallest breakpoint greater than line. Since breakpoints is sorted and unique, you can use binary search (upper bound) for O(log n) per action, or keep a moving index. The pitfall is the moving index. "next" can skip over or land on a breakpoint, so a pointer that only advances on "continue" goes stale. Example 3 shows it: you land on line 2 via next, which is a breakpoint, and continue must go to 4, not 2. Use strictly greater, never greater or equal. A linear scan per action also works for small inputs, but binary search is safer. If the live OA scrambles your memory of bisect_right, StealthCoder is the hedge that hands you the clean version.
The honest play: practice the pattern, and have StealthCoder ready for the one you didn't see coming.
You can drill Debugger Breakpoint Actions 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. Built for the candidate who saw this exact problem leak two days before his OA and wondered if anyone had a play.
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Debugger Breakpoint Actions FAQ
How hard is the TikTok Debugger Breakpoint Actions problem really?+
Easy. It's a simulation with one lookup rule. The difficulty is off-by-one thinking, specifically strictly after versus at or after. If you trace the three given examples by hand before submitting, you'll catch nearly every bug.
What's the trick to the "continue" action?+
Find the first breakpoint strictly greater than the current line. Because the array is sorted, use binary search with an upper bound. Don't keep a pointer that only moves on continue, since next actions can move you past breakpoints.
Do I need binary search or is a linear scan fine?+
A linear scan per continue is correct and fine for small inputs. Binary search is safer if actions and breakpoints are large, since it's O(log n) per lookup. In Python, bisect_right on the current line gives the index directly.
What edge cases should I test?+
Test a continue right after landing on a breakpoint, since it must skip that same line. Test a next that lands exactly on a breakpoint. Test an empty actions list, which should return 1. The constraints guarantee valid actions, so skip bounds checks.
How do I prepare for this in 48 hours?+
Write the simulation once from scratch, then run all three examples by hand. Practice upper-bound binary search so you don't fumble it under a timer. This pattern shows up often in OAs as a warm-up question, so speed and clean code matter more than cleverness.