Formatted question description: https://leetcode.ca/all/2150.html

# 2150. Find All Lonely Numbers in the Array (Medium)

You are given an integer array nums. A number x is lonely when it appears only once, and no adjacent numbers (i.e. x + 1 and x - 1) appear in the array.

Return all lonely numbers in nums. You may return the answer in any order.

Example 1:

Input: nums = [10,6,5,8]
Output: [10,8]
Explanation:
- 10 is a lonely number since it appears exactly once and 9 and 11 does not appear in nums.
- 8 is a lonely number since it appears exactly once and 7 and 9 does not appear in nums.
- 5 is not a lonely number since 6 appears in nums and vice versa.
Hence, the lonely numbers in nums are [10, 8].
Note that [8, 10] may also be returned.


Example 2:

Input: nums = [1,3,5,3]
Output: [1,5]
Explanation:
- 1 is a lonely number since it appears exactly once and 0 and 2 does not appear in nums.
- 5 is a lonely number since it appears exactly once and 4 and 6 does not appear in nums.
- 3 is not a lonely number since it appears twice.
Hence, the lonely numbers in nums are [1, 5].
Note that [5, 1] may also be returned.


Constraints:

• 1 <= nums.length <= 105
• 0 <= nums[i] <= 106

Similar Questions:

## Solution 1. Hash Map

// OJ: https://leetcode.com/problems/find-all-lonely-numbers-in-the-array/
// Time: O(N)
// Space: O(U) where U is the number of unique elements in A
class Solution {
public:
vector<int> findLonely(vector<int>& A) {
unordered_map<int, int> m;
for (int n : A) m[n]++;
vector<int> ans;
for (int n : A) {
if (m[n] == 1 && m.count(n + 1) == 0 && m.count(n - 1) == 0) {
ans.push_back(n);
}
}
return ans;
}
};


## Discuss

https://leetcode.com/problems/find-all-lonely-numbers-in-the-array/discuss/1711230/C%2B%2B-Hash-Map-O(N)