Find All Numbers Disappeared in an Array

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

Find all the elements of [1, n] inclusive that do not appear in this array.

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

Example:

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

思路：將數字與下標對應起來，若不匹配的說明當前值缺失;

JAVA CODE

class Solution {    public List<Integer> findDisappearedNumbers(int[] nums) {        List<Integer> list = new ArrayList<>();        int[] mm = new int[nums.length];        for(int i = 0; i < nums.length; i++){            mm[nums[i]-1] = nums[i];        }        for(int i = 0; i < nums.length; i++){            if(mm[i]-1!=i)                list.add(new Integer(i+1));        }        return list;    }}

 

Find All Numbers Disappeared in an Array