How to Identify a Missing Number in an Integer Array?

What is the best way to identify a missing number in an integer array?

int findMissingNumber(int arr[], int n) {
    int total = (n + 1) * (n + 2) / 2;
    int sum = 0;
    for (int i = 0; i < n; i++) {
        sum += arr[i];
    }
    return total - sum;
}

Finding a missing number in an integer array involves calculating the expected sum of a complete range of numbers and comparing it against the actual sum of the array elements. This method is efficient and effective for arrays containing distinct integers from 1 to n where one number is missing.

int findMissingNumber(int arr[], int n) {
    int total = (n + 1) * (n + 2) / 2;
    int sum = 0;
    for (int i = 0; i < n; i++) {
        sum += arr[i];
    }
    return total - sum;
}

Causes

• The array contains distinct integers ranging from 1 to n, but one number is absent.
• The integers are not stored in sequential order.

Solutions

• Calculate the expected sum using the formula for the sum of the first n natural numbers, which is (n*(n + 1))/2.
• Iterate through the array to compute the actual sum of its elements. The difference between the expected sum and the actual sum gives the missing number.

Mistake: Calculating the total with the wrong number of elements.

Solution: Ensure you are using the correct formula for n, as it should represent the highest number expected in the array.

Mistake: Not iterating through the entire array or missing elements prevention.

Solution: Confirm that your loop covers all indices from 0 to n-1 accurately.