46. Permutations

Given an array nums of distinct integers, return all the possible permutations. You can return the answer in any order.

Example 1:

Input: nums = [1,2,3]
Output: [[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]]

Example 2:

Input: nums = [0,1]
Output: [[0,1],[1,0]]

Example 3:

Input: nums = [1]
Output: [[1]]

Constraints:

• 1 <= nums.length <= 6
• -10 <= nums[i] <= 10
• All the integers of nums are unique.

# @lc code=start
using LeetCode

permutation(nums::Vector{Int}) = permutation!(copy(nums))
function permutation!(nums::Vector{Int})
    sort!(nums)
    res = Vector{Vector{Int}}()
    n = length(nums)
    sizehint!(res, factorial(n))
    function dfs(nums::Vector{Int}, path::Vector{Int}, used::Vector{Bool}, len::Int)
        if len == n # alternatively, len = sum(used)
            push!(res, copy(path))
            return nothing
        end
        for i in 1:n
            used[i] && continue
            used[i] = true
            path[len + 1] = nums[i]
            dfs(nums, path, used, len + 1)
            used[i] = false
        end
    end
    dfs(nums, Vector{Int}(undef, n), fill(false, n), 0)
    return res
end
# @lc code=end

permutation! (generic function with 1 method)

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