268. Missing Number

Problem

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:

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:

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:

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.

  Constraints:

• n == nums.length

• 1 <= n <= 10^4

• 0 <= nums[i] <= n

• All the numbers of nums are unique.

  Follow up: Could you implement a solution using only O(1) extra space complexity and O(n) runtime complexity?

Solution

/**
 * @param {number[]} nums
 * @return {number}
 */
var missingNumber = function(nums) {
    let expectedSum = nums.length*(nums.length + 1)/2
    let actualSum = nums.reduce((a, b) => a + b, 0)
    let missingNumber = expectedSum - actualSum

    return missingNumber 
};

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).