sclass FreeList {
  MultiMap<Int, IntRange> byLength = treeMultiMap();
  TreeSet<IntRange> inOrder = new(intRangeComparatorByStart());
  
  void add(IntRange r) {
    inOrder.
  }
  
  void remove(IntRange r) {
  }
  
  IntRange findFreeSpace(int minSize) {
    Map.Entry<Int. L<IntRange>> e = byLength.ceilingEntry(minSize);
    ret e == null ? null : first(e.getValue());
  }
}