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Permutations at Airbnb — Interview Guide

The problem at Airbnb

Given a list of distinct integers, return all possible permutations.

Airbnb uses this problem to assess product craft and full-stack ownership. Expect Airbnb-specific follow-ups that tie the solution back to production reasoning and the company's engineering bar.

Key concepts

Swap-based backtracking produces permutations in place with O(n) extra space for the recursion.
Pick-based backtracking (used/unused set) is more intuitive but uses more memory.
For duplicates, sort and skip a duplicate when the identical previous element was not used in this branch.

Approach

def permute(nums):
    res = []
    def bt(first):
        if first == len(nums):
            res.append(nums[:]); return
        for i in range(first, len(nums)):
            nums[first], nums[i] = nums[i], nums[first]
            bt(first + 1)
            nums[first], nums[i] = nums[i], nums[first]
    bt(0)
    return res

What Airbnb looks for

Product and design sense — you care about the user experience.
Full-stack comfort (frontend + backend) for many roles.
Craft and code quality.
Alignment with 'belonging' and host/ guest empathy.

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