算法设计与应用基础作业第三周

448. Find All Numbers Disappeared in an Array          

Description：

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]

分析：

   这道题的意思很简单，给出一个数组，输出没有出现过的数字。

   但是有一个需要注意的要点，那就是对于runtime的要求：O（n）！

My C++ code：

class Solution {public:    vector<int> findDisappearedNumbers(vector<int>& nums) {        int length = nums.size() ;        vector<bool> m(length, false);        vector<int> res;        for(int num : nums)        {            m[num-1] = true;        }        for(int i = 0; i < length; ++i)        {            if(!m[i])                res.push_back(i+1);        }        return res;    }};