# Find the missing and repeated element in the given array

In this particular question we are given an array of the size N with the values also in the range 1 to N (both inclusive). Each number in the range 1 to N appears exactly once except for X and Y. The number X appears twice whereas the number Y is missing. The task is to find the repeating and the missing number A and B in the given read only array.

This question can be solved using hashing technique. Using this technique we can store the count of each element between 1 to N. Now the element with the count 2 is the repeating element and the element with the count 0 is the missing element.

#### Approach

- Create an hash array of size N+1.
- Initialize the values of each element in the temp array to 0.
- Iterate all the elements of the input array and update the values of hash array :

- hash[a[i]] = hash[a[i]] + 1

- Iterate the hash array to return the repeating and missing element :

- If hash[i] == 2, it implies that ‘i’ is the repeating element
- If hash[i] == 0, it implies that ‘i’ is the missing element

Here, hash = hash array, a = given array

#### Complexity

- Time Complexity: O(N)
- Space Complexity: O(N)

Where N is the size of the given array

#### Java Code

```
import java.util.Arrays;
public class FindNumbers {
public static int[] findMissingRepeatingNumbers(int[] a) {
int n = a.length; // size of the array
int[] hash = new int[n + 1]; // hash array
//update the hash array:
for (int i = 0; i < n; i++) {
hash[a[i]]++;
}
//Find the repeating and missing number:
int repeating = -1, missing = -1;
for (int i = 1; i <= n; i++) {
if (hash[i] == 2) repeating = i;
else if (hash[i] == 0) missing = i;
if (repeating != -1 && missing != -1)
break;
}
int[] ans = {repeating, missing};
return ans;
}
public static void main(String[] args) {
int[] a = {3, 1, 2, 5, 4, 6, 7, 5};
int[] ans = findMissingRepeatingNumbers(a);
System.out.println("Input array is " + Arrays.toString(a));
System.out.println("The repeating and missing numbers are: {"
+ ans[0] + ", " + ans[1] + "}");
}
}
```

Output

Input array is [3, 1, 2, 5, 4, 6, 7, 5]

The repeating and missing numbers are: {5, 8}