Day33.java

/*Array Duplicates
Given an array arr[] of size n, containing elements from the range 1 to n, and each element appears at most twice, return an array of all the integers that appears twice.

Note: You can return the elements in any order but the driver code will print them in sorted order.

Examples:

Input: arr[] = [2, 3, 1, 2, 3]
Output: [2, 3] 
Explanation: 2 and 3 occur more than once in the given array.
Input: arr[] = [3, 1, 2] 
Output: []
Explanation: There is no repeating element in the array, so the output is empty. */
/* import java.util.*;

class Solution {
    public ArrayList<Integer> findDuplicates(int[] arr) {
        ArrayList<Integer> result = new ArrayList<>();
        int n = arr.length;

        for (int i = 0; i < n; i++) {
            int index = Math.abs(arr[i]) - 1;

            if (arr[index] < 0) {
                result.add(index + 1);
            } else {
                arr[index] = -arr[index];
            }
        }

        return result;
    }
}
*/
/*⏱ Time & Space Complexity

Time Complexity: O(n)

Space Complexity: O(1) (excluding output list) */