448. Find all Numbers Disappeared in an Array

📝 Problem Details

• Title: 448. Find all Numbers Disappeared in an Array
• Link: https://leetcode.com/problems/find-all-numbers-disappeared-in-an-array/
• Difficulty: Easy
• Tags/Categories: Arrays Hashmap

💭What Were My Initial Thoughts?

sorting the array could be useful
using a hashmap could be a way to avoid the need to sort

🤔What Did I Struggle With?

~

💡 Explanation of Solution

- initialize and populate an unordered set with all values in nums
- interate through the array, starting with an index i = 1
- check if i exists in the set, if it doesnt then push i into a results vector
- return result

⌛ Complexity Analysis

Time Complexity: O(n)
Space Complexity: O(n)

💻 Implementation of Solution

class Solution {
 
public:
    vector<int> findDisappearedNumbers(vector<int>& nums) {
        unordered_set<int> set(nums.begin(), nums.end());
        vector<int> result;
 
        for(int i=1; i <= nums.size(); i++) {
            if(set.find(i) == set.end()) {
                result.push_back(i);
            }
        }
        return result;
    }
};