268. Missing Number – Leetcode Solutions

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.

from typing import List

class Solution:
    def missingNumber(self, nums: List[int]) -> int:
        # Calculate the expected sum of numbers in the range [0, n]
        # This is based on the formula for the sum of the first n natural numbers: n*(n+1)/2
        n = len(nums)  # The length of the input array gives the value of n
        expected_sum = n * (n + 1) // 2  # The expected sum of numbers from 0 to n
        
        # Calculate the actual sum of the numbers in the input array
        actual_sum = sum(nums)
        
        # The missing number will be the difference between the expected sum and the actual sum
        return expected_sum - actual_sum

#include <vector>
using namespace std;

class Solution {
public:
    int missingNumber(vector<int>& nums) {
        // Get the size of the input array, which is n
        int n = nums.size();
        
        // Calculate the expected sum of numbers in the range [0, n]
        // This is based on the sum formula: n*(n+1)/2
        int expected_sum = n * (n + 1) / 2;
        
        // Calculate the actual sum of the numbers in the input array
        int actual_sum = 0;
        for (int num : nums) {
            actual_sum += num;
        }
        
        // The missing number is the difference between the expected sum and the actual sum
        return expected_sum - actual_sum;
    }
};

var missingNumber = function(nums) {
    // Get the length of the input array, which is n
    const n = nums.length;
    
    // Calculate the expected sum of numbers in the range [0, n]
    // The formula for the sum of the first n numbers is: n * (n + 1) / 2
    const expectedSum = n * (n + 1) / 2;
    
    // Calculate the actual sum of the numbers in the input array
    let actualSum = 0;
    for (let i = 0; i < nums.length; i++) {
        actualSum += nums[i];
    }
    
    // The missing number is the difference between the expected sum and the actual sum
    return expectedSum - actualSum;
};

class Solution {
    public int missingNumber(int[] nums) {
        // Get the length of the input array, which is n
        int n = nums.length;
        
        // Calculate the expected sum of numbers in the range [0, n]
        // The formula for the sum of the first n natural numbers is: n * (n + 1) / 2
        int expectedSum = n * (n + 1) / 2;
        
        // Calculate the actual sum of the numbers in the input array
        int actualSum = 0;
        for (int num : nums) {
            actualSum += num;
        }
        
        // The missing number is the difference between the expected sum and the actual sum
        return expectedSum - actualSum;
    }
}