find-all-duplicates-in-an-array_442.py

# Given an integer array nums of length n where all the integers of nums are in the range [1, n] and each integer appears once or twice, return an array of all the integers that appears twice.

# You must write an algorithm that runs in O(n) time and uses only constant extra space.

# Example 1:

# Input: nums = [4,3,2,7,8,2,3,1]
# Output: [2,3]
# Example 2:

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

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


# Constraints:

# n == nums.length
# 1 <= n <= 105
# 1 <= nums[i] <= n
# Each element in nums appears once or twice.

# ---------------------------------------Runtime 258 ms Beats 71.00% Memory 25.69 MB Beats 5.99%---------------------------------------

from typing import List


class Solution:
    def findDuplicates(self, nums: List[int]) -> List[int]:
        res = set()
        nums_set = set()
        for num in nums:
            num in nums_set and res.add(num)
            nums_set.add(num)
        return res