448. Find all Numbers disappeared in an Array

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

Find all the elements of [1,N] inclusive The does not appear in this array.

Could do it without extra space and in O (n) runtime? Assume the returned list does not count as extra space.

Example:

Input: [4,3,2,7,8,2,3,1] Output: [5,6]

The main idea is given an array with a maximum value of N, N= size of arrayThe element appears once or two times, and there is no occurrence to find the element that does not appear. The topic requires no additional space, and the time complexity is O (n). This method is quite ingenious. There's an important clue to this question.The maximum value of the element is the length of the array,First iterate through the array, using theNums[nums[i]-1] =-nums[nums[i]-1]The value is negative, and in the second traversal, the number that is not negative is the value that does not appear.

classSolution { PublicList<integer> Finddisappearednumbers (int[] nums) {List<Integer> result =NewArraylist<integer>();  for(inti = 0; i < nums.length; i++)        {            intTMP = Math.Abs (Nums[i])-1;//Index            if(Nums[tmp] > 0) nums[tmp] =-Nums[tmp]; }         for(inti = 0;i < nums.length; i++)            if(Nums[i] > 0) l.add (i + 1)); returnresult; }}

448. Find all Numbers disappeared in an Array