MediumCoding

Car Fleet

Asked at

PhonePe

1Give yourself 5 minutes

2Answer out loud, not in your head

3Then compare with the answer below

Stuck? Show a way to structure it+

01Pair each position with speed.
02Sort cars by position descending.
03Compute remaining arrival time.
04Keep the slowest time seen ahead.
05Count a fleet only when time increases.

Reference answer

Sort cars from closest to the target to farthest. A car's independent arrival time is (target - position) / speed. Scan in that order while retaining the largest arrival time among fleets already ahead. If the current car's time is less than or equal to that value, it catches the fleet ahead before the target and inherits that fleet time; otherwise it starts a new fleet and becomes the new maximum. Use floating-point or compare fractions carefully if precision matters. The important invariant is that fleet arrival times encountered from front to back are strictly increasing. Do not simulate positions over time. Sorting dominates at O(n log n) time; the scan is O(n), with O(n) storage for pairs or O(1) extra beyond sorting in place.

Then expect these follow-ups

How would you avoid floating-point comparisons?
Tests: follow-up reasoning
Why can cars never split after forming a fleet?
Tests: correctness reasoning

Free to read · better with Enzo

Practice this out loud with Enzo

Enzo runs it as a mock interview, pushes back with follow-ups, and grades you on the rubric.

Continue with Enzo Sign up free

Next question