Missing Number

Given an array containing n distinct numbers taken from 0, 1, 2, ..., n, find the one that is missing from the array.

Example 1 Input: [3,0,1] Output: 2

Example 2 Input: [9,6,4,2,3,5,7,0,1] Output: 8

Solution : Gauss' Formula

We can use the formula to calculate the total sum of 0..n

int missingNumber(vector<int>& nums) {
    int totalSum = nums.size() * (nums.size() + 1) / 2;
    int sum = 0;
    for(auto num: nums) {
        sum += num;
    }
    return totalSum - sum;
}