Day43.java

/*Missing in Array
You are given an array arr[] of size n - 1 that contains distinct integers in the range from 1 to n (inclusive). This array represents a permutation of the integers from 1 to n with one element missing. Your task is to identify and return the missing element.

Examples:

Input: arr[] = [1, 2, 3, 5]
Output: 4
Explanation: All the numbers from 1 to 5 are present except 4.
Input: arr[] = [8, 2, 4, 5, 3, 7, 1]
Output: 6
Explanation: All the numbers from 1 to 8 are present except 6.
Input: arr[] = [1]
Output: 2
Explanation: Only 1 is present so the missing element is 2. */
/*class Solution {
    int missingNum(int arr[]) {
        int n = arr.length + 1;

        long expectedSum = (long) n * (n + 1) / 2;
        long actualSum = 0;

        for (int num : arr) {
            actualSum += num;
        }

        return (int)(expectedSum - actualSum);
    }
}
 */
/*class Solution {
    int missingNum(int arr[]) {
        int n = arr.length + 1;
        int xor = 0;

        for (int i = 1; i <= n; i++) {
            xor ^= i;
        }

        for (int num : arr) {
            xor ^= num;
        }

        return xor;
    }
}
 */
/*⏱ Complexity 

Time Complexity: O(n)

Space Complexity: O(1) */