LeetCode 442 Find All Duplicates in an Array (思维)

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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]

题目链接：https://leetcode.com/problems/find-all-duplicates-in-an-array/

题目分析：第三道一样的题了，同Find All Numbers Disappeared in an Array

class Solution {
    
    public void swap(int[] nums, int i, int j) {
        int tmp = nums[i];
        nums[i] = nums[j];
        nums[j] = tmp;
    }
    
    public List<Integer> findDisappearedNumbers(int[] nums) {
        List<Integer> ans = new ArrayList<>();
        int pos = 0;
        while (pos < nums.length) {
            while (nums[pos] != pos + 1 && nums[pos] != nums[nums[pos] - 1]) {
                swap(nums, pos, nums[pos] - 1);
            }
            pos++;
        }
        for (int i = 0; i < nums.length; i++) {
            if (nums[i] != i + 1) {
                ans.add(i + 1);
            }
        }
        return ans;
    }
}

// 4 3 2 7 8 2 3 1
// 7 3 2 4 8 2 3 1
// 3 3 2 4 8 2 7 1
// 2 3 3 4 8 2 7 1
// 3 2 3 4 8 2 7 1
// 3 2 3 4 1 2 7 8
// 1 2 3 4 3 2 7 8