Missing Number Problem

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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.

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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.

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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.

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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.

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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;
    }
};