In computer programming, a rope, or cord, is a data structure composed of smaller strings that is used to efficiently store and manipulate a very long string. For example, a text editing program may use a rope to represent the text being edited, so that operations such as insertion, deletion, and random access can be done efficiently. Description A rope is a type of binary tree where each leaf (end node) holds a string and a length (also known as a "weight"), and each node further up the tree holds the sum of the lengths of all the leaves in its left subtree. A node with two children thus divides the whole string into two parts: the left subtree stores the first part of the string, the right subtree stores the second part of the string, and a node's weight is the length of the first part. For rope operations, the strings stored in nodes are assumed to be constant immutable objects in the typical nondestructive case, allowing for some copy-on-write behavior. Leaf nodes are usually implemented as basic fixed-length strings with a reference count attached for deallocation when no longer needed, although other garbage collection methods can be used as well. Operations In the following definitions, N is the length of the rope. Collect Leaves Definition: Create a stack S and a list L. Traverse down the left-most spine of the tree until you reach a leaf l', adding each node N to S. Add l' to L. The parent of l' (p) is at the top of the stack. Repeat the procedure for p's right subtree. final class InOrderRopeIterator implements Iterator<RopeLike> { private final Deque<RopeLike> stack; InOrderRopeIterator(@NonNull RopeLike root) { stack = new ArrayDeque<>(); var c = root; while (c != null) { stack.push(c); c = c.getLeft(); } } @Override public boolean hasNext() { return stack.size() > 0; } @Override public RopeLike next() { val result = stack.pop(); if (!stack.isEmpty()) { val parent = stack.pop(); val right = parent.getRight(); if (right != null) { stack.push(right); var cleft = right.getLeft(); while (cleft != null) { stack.push(cleft); cleft = cleft.getLeft(); } } } return result; } } Rebalance Definition: Collect the set of leaves L and rebuild the tree from the bottom-up. static boolean isBalanced(RopeLike r) { val depth = r.depth(); if (depth >= FIBONACCI_SEQUENCE.length - 2) { return false; } return FIBONACCI_SEQUENCE[depth + 2] <= r.weight(); } static RopeLike