Interview Question for Software Engineer at eBay:

h = new HashMap();
for (int i=0; i < a.length; ++i) {
  h.put(a[i], i);
}
for (int i=0; i < h.keys.length; ++i) {
  int match = sum - h.keys[i];
  if (h.get(match) != null) {
    print h.keys[i] + "," + h.keys[match];
  }
}