#permutations

8 permutations interview questions, asked at Amazon, Microsoft, Uber and 3 more companies. Last asked Oct 2026.

Sorting complexity: beat O(n²), then design the worst correct sortCodingA verbal round with no coding, asked as a quick series: 1. Explain a sorting algorithm faster than O(n²) and why it is faster; be ready for quicksort's worst case. 2. Name or…
Last asked Oct 2026
Largest permutation after sorting one fixed-length windowCodingYou get a permutation of 1 to n and a window size w. Exactly once, choose a contiguous window of exactly w elements and sort the elements inside it. Return the lexicographically…
Last asked Oct 2026
Every ordering of N students in a line, then in a circleCodingPrint every way N students can stand in a line. Follow-up: they stand in a circle instead, where rotations of the same arrangement count once.
Last asked Apr 2026
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Balanced prefixes in a permutationCodingYou are given a permutation p of length n: every integer from 1 to n appears exactly once, in some order. Call a number k (with 1 <= k <= n) balanced if some contiguous subarray…
Last asked Apr 2026
Next permutationCodingRearrange an array of numbers into the next permutation in lexicographic order, in place with constant extra memory; if it is the last permutation, wrap around to the smallest.
Last asked Feb 2026
Count valid 24-hour times from four digitsCodingWrite a function countvalidtimes(a, b, c, d) that takes four digits (each an integer from 0 to 9). Arrange all four digits as HH:MM on a 24-hour clock, using each given digit…
Valid date from three integers in any orderCodingYou are given three integers a, b and c. Their order is unknown: any one of them may be the year, the month or the day. This covers formats such as yyyy-MM-dd, MM-dd-yyyy and…
Which prefixes of 1..n appear as a contiguous blockCodingYou are given an array p of length n that is a permutation of the integers 1..n (each value appears exactly once). For every k from 1 to n, decide whether p has a contiguous…