Missing number

missingNumber.js

/**
 * @param {number[]} nums
 * @return {number}
 */
var missingNumber = function(nums) {
    let sum = ((nums.length) * (nums.length + 1)) / 2;
    let sum2 = 0;
    for(let i=0; i<nums.length; i++) {
        sum2 += nums[i];
    }

    return sum - sum2;
};

// Find the sum of all numbers in the range by the formula (n*(n+1)) / 2
// Find the sum of all numbers in the array
// Subtract both sums to get the answer