LeetCode 268 Missing Number

Coding challenge

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.

Constraints

n == nums.length 1 <= n <= 104 0 <= nums[i] <= n All the numbers of nums are unique.

examples:

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.

---------

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.

Breakdown and Discussion of challenge

Given an unsorted array of integer values, we need to check all the numbers and see which number is the missing from the given range. For challenges that require finding something within the array, against some factor, in this case being the array's range of numbers, I like to immediately think of using an object to map the array's values to the object. This method allows for the object to have all the values and then I can check against the array to see what is missing, compare, check for duplicates ect..

Approach

Within the function we create an object missingNum and an array result. Use a for loop to iterate through the array mapping each array's index to the object keys and setting each key's value to false. Create a second loop to set to true each object key's that is in the object using the array's values. A last for loop is create, this time a for in loop, grabbing each key from the object and using an if statement asking: missingNum[key] === false take the result array and push the key with false value to it. Now the function will return result[0] the fist element in the array.

time complexity

O(n).

space complexity

O(n).

Code

function missingNumber(nums) {
    const missingNum = {};
    const result = [];

    for (let i = 0; i <= nums.length; i++) {
        missingNum[i] = false;
    }
    for (let i = 0; i < nums.length; i++) {
        missingNum[nums[i]] = true;
    }
    for (const key in missingNum) {
        if (missingNum[key] === false) result.push(key)
    }


    return result[0];
};

Road to 170

LC: 2

This is the second Leetcode challenge of the 170 challenges from the LeetCode Patterns by Sean Prashad