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# 268. Missing Number

## Description

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.*

**Follow up:** Could you implement a solution using only `O(1)`

extra space complexity and `O(n)`

runtime complexity?

**Example 1:**

Input:nums = [3,0,1]Output:2Explanation: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:2Explanation: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:8Explanation: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.

**Example 4:**

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

**Constraints:**

`n == nums.length`

`1 <= n <= 10`

^{4}`0 <= nums[i] <= n`

- All the numbers of
`nums`

are**unique**.