# Missing Number Problem

## Description

LeetCode Problem 268.

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:

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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:

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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:

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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.

Example 4:

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Input: nums = [0]
Output: 1
Explanation: 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.

## Sample C++ Code

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class Solution {
public:
int missingNumber(vector<int>& nums) {
int curr_sum = 0;
int actual_sum = 0;
for (int i = 0; i < nums.size(); i ++) {
curr_sum += nums[i];
actual_sum += i;
}
return actual_sum + nums.size() - curr_sum;
}
};