LeetCode 442. Find All Duplicates in an Array

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题目

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:

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

Output:
[2,3]

思路

Same with 287.

代码

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class Solution(object):
    def findDuplicates(self, nums):
        """
        :type nums: List[int]
        :rtype: List[int]
        """
        res = []
        for num in nums:
	        if nums[abs(num)-1]>0:
		        nums[abs(num)-1]=-nums[abs(num)-1]
	        else:
		        res.append(abs(num))
        return res