Missing Number

def missingNumber(nums: list[int]) -> int:
    n = len(nums)
    expected_sum = n * (n + 1) // 2
    actual_sum = sum(nums)
    return expected_sum - actual_sum

class Solution {
public:
    int missingNumber(vector<int>& nums) {
        int n = nums.size();
        long long expectedSum = (long long)n * (n + 1) / 2;
        long long actualSum = 0;
        for (int num : nums) {
            actualSum += num;
        }
        return expectedSum - actualSum;
    }
};

function missingNumber(nums: number[]): number {
    const n = nums.length;
    const expectedSum = (n * (n + 1)) / 2;
    const actualSum = nums.reduce((a, b) => a + b, 0);
    return expectedSum - actualSum;
}