// return index and value
static Pair<Int> minOfIntArray_withIndex(int[] a) {
  if (a == null || a.length == 0) null;
  int n = a.length, x = a[0], best = 0;
  for (int i = 1; i < n; i++) {
    int y = a[i];
    if (y < x) {
      x = y;
      best = i;
    }
  }
  ret pair(best, x);
}