*Last updated: Nov 27, 2022*

Difficulty | Runtime | Faster_than | Memory | Lesser_than |
---|---|---|---|---|

easy | 115 ms | 50.9 % | 44.5 mb | 44.12 % |

# 268. Missing Number

Given an array nums containing n distinct numbers in the range [0, n], return the only number in the range that is missing from the array.

**Example 1**:
Input: nums = [3,0,1]
Output: 2
Explanation: n = 3 since there are 3 numbers, so all numbers are in the range [0,3]. 2 is the missing number in the range since it does not appear in nums.

**Example 2**:
Input: nums = [0,1]
Output: 2
Explanation: n = 2 since there are 2 numbers, so all numbers are in the range [0,2]. 2 is the missing number in the range since it does not appear in nums.

**Example 3**:
Input: nums = [9,6,4,2,3,5,7,0,1]
Output: 8
Explanation: n = 9 since there are 9 numbers, so all numbers are in the range [0,9]. 8 is the missing number in the range since it does not appear in nums.

**Constraints**:

- n == nums.length
- 1 <= n <= 104
- 0 <= nums[i] <= n
- All the numbers of nums are unique.

**Follow up**: Could you implement a solution using only O(1) extra space complexity and O(n) runtime complexity?

## Solution:

```
/**
* @param {number[]} nums
* @return {number}
*/
var missingNumber = function(nums) {
var sum = function(n) {
return n*(n + 1)/2;
}
var n = nums.length;
var sumOfArr = 0;
for(var i = 0; i < nums.length; i++) {
sumOfArr += nums[i];
}
return sum(n) - sumOfArr
};
```