Find All Duplicates In An Array · Interview Problem

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Leetcode

Medium

Arrays

Bit Manipulation

Find All Duplicates In An Array

Find every value that appears exactly twice in an array of integers.

Acceptance 0%

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Problem Statement

Problem

Given an integer array nums of length n where each value is in the range 1 to n, return all numbers that appear exactly twice.

You should aim for an algorithm that runs in linear time and uses only constant extra space, excluding the output array.

Notes

A number may appear once or twice, but not more than twice.
The order of the returned duplicates does not matter.

Input Format

An integer array nums.
nums.length = n.
Each nums[i] is an integer in the range 1..n.

Output Format

Return an array containing all values that appear exactly twice in nums.
The order of elements in the output does not matter.

Constraints

$1 \le n \le 10^5$
$1 \le nums[i] \le n$
Each element appears once or twice.
Aim for $O(n)$ time and $O(1)$ extra space, excluding output storage.

Examples

Sample cases returned by the problem API.

Example 1

Input

nums = [4,3,2,7,8,2,3,1]

Output

[2,3]

Explanation

Both 2 and 3 appear exactly twice. The order of the answer is not important.

Example 2

Input

nums = [1,1,2]

Output

[1]

Explanation

Only 1 appears twice.

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