Find two pair of index or two sum of index in a list

Problem statement: Given an array of integers, return indices of two numbers such that they add up to a specific target.
e.g. - arr[] = { 4, 6, 5, -10, 8, 5, 20 };
target = 10
Output: [4,6] , [5,5], [-10,20]

Note: You may assume that each input would have exactly one solution, and you may not use the same element twice.

1. import java.util.HashMap;
2. import java.util.Map;
3. 
   
4. public class IndexOfTwoPair{
5. 
   
6. public static void main(String[] args) {
7. int a[] = { 4, 6, 5, -10, 8, 5, 20 };
8. int n = 10;
9. int idx[] = indexOfTwoSum(a, n);
10. for (int i : idx) {
11. System.out.print(i + " ");
12. }
13. }
14. public static int[] indexOfTwoSum(int nums[], int target) {
15. // array to return the result
16. int arr[] = new int[2];
17. 
    
18. // map for num and index pair
19. Map<Integer, Integer> map = new HashMap<Integer, Integer>();
20. 
    
21. // scan the array element
22. for (int i = 0; i < nums.length; i++) {
23. // check if map has an element which is equal to difference
24. // between target and current element
25. Integer val = map.get(target - nums[i]);
26. if (val == null) {
27. // no match found, add current element & index to map
28. map.put(nums[i], i);
29. } else {
30. // match found, update the index values
31. arr[0] = val;
32. arr[1] = i;
33. }
34. }
35. return arr;
36. }
37. }

Output:

3 6