Find elements with sum equal to the sum of their indexes

Problem:
Write a method which takes an array input and returns true if the sum of any two elements is equal to the sum of the corresponding indices. Like if for an array the sum of values at any two indices i and j is equal to the sum of i and j.

Solution:
Since we know we are looking for pairs where x+y = A[x] + A[y], by simple algebra, you can also look for x-A[x] = A[y]-y

public static ArrayList<ArrayList<Integer>> findSums(int[] A) {
  // Look for pairs where  x - A[x] == A[y] - y
  ArrayList<ArrayList<Integer>> soln = new ArrayList<ArrayList<Integer>>();
  HashMap<Integer,Integer> h = new HashMap<Integer,Integer>();
  
  for (int x = 0; x < A.length; x++) {
   h.put(x-A[x],x);
  }
  
  for (int y = 0; y < A.length; y++) {
   if (h.containsKey(A[y]-y)) {
    int x = h.get(A[y]-y);
    if (y != x) {
     ArrayList<Integer> pair= new ArrayList<Integer>();
     pair.add(x);
     pair.add(y);
     soln.add(pair);
    }
   }
  }
  
  return soln;
}

Complexity:

time - O(n)
space - O(n)

Links and credits:
http://www.careercup.com/question?id=5705699820568576