442. Find All Duplicates in an Array

Given an array of integers, 1 ≤ a[i] ≤ n ( n = size of array), some elements appear twice and others appear once.

Find all the elements that appear twice in this array.

Could you do it without extra space and in O( n ) runtime?

Example:

Input:
[4,3,2,7,8,2,3,1]

Output:
[2,3]

# @lc code=start
using LeetCode

function find_duplicates_442(nums::Vector{Int})
    res = Int[]
    for num in nums
        absn = abs(num)
        nums[absn] < 0 ? push!(res, absn) : (nums[absn] = -nums[absn])
    end
    return res
end
# @lc code=end

find_duplicates_442 (generic function with 1 method)

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