web/wavl.js

class WAVLTree extends AVLTree {
    isCorrectNode(node, recursive) {
        if (!node) {
            return true;
        }

        nodeDifferences(node).forEach((childRank) => {
            if ([1, 2].indexOf(childRank) == -1) {
                return false;
            }
        });

        if (node.type() == LEAF) {
            return node.rank == 0;
        }

        recursive = recursive ?? true;
        return (
            !recursive ||
            (this.isCorrectNode(node.left) && this.isCorrectNode(node.right))
        );
    }

    fixDelete(x, y, z, reversed, rotatingAroundRoot, rotateLeft, rotateRight) {
        let newRoot = x;
        let [v, w] = [y.left, y.right];

        if (reversed) {
            [v, w] = [w, v];
        }

        let wDiff = nodeDifference(w, y);

        if (wDiff == 1 && y.parent) {
            newRoot = rotateLeft(y.parent);
            if (rotatingAroundRoot) {
                this.root = newRoot;
            }
            this.record(
                "Final step of deletion rebalance: single rotation by parent of y",
                y.parent
            );

            y.promote();
            this.record("Final step of deletion rebalance: promotion of y", y);

            z.demote();
            this.record("Final step of deletion rebalance: demotion of z", z);

            if (z.type() == LEAF) {
                z.demote();
                this.record(
                    "Final step of deletion rebalance: demotion of leaf z",
                    z
                );
            }
        } else if (wDiff == 2 && v && v.parent) {
            rotateRight(v.parent);
            this.record(
                "Final step of deletion rebalance: first of double rotation by parent of v",
                v.parent
            );

            newRoot = rotateLeft(v.parent);
            if (rotatingAroundRoot) {
                this.root = newRoot;
            }
            this.record(
                "Final step of deletion rebalance: second of double rotation by parent of v",
                v.parent
            );

            v.promote().promote();
            this.record(
                "Final step of deletion rebalance: double promotion of v",
                v
            );

            y.demote();
            this.record("Final step of deletion rebalance: demotion of y", y);

            z.demote().demote();
            this.record(
                "Final step of deletion rebalance: double demotion of z",
                z
            );
        }
    }

    bottomUpDelete(x, parent) {
        let xDiff = nodeDifference(x, parent);
        if (xDiff != 3 || !parent) {
            return;
        }

        let y = parent.left === x ? parent.right : parent.left;
        let yDiff = nodeDifference(y, parent);

        while (
            parent &&
            xDiff == 3 &&
            y &&
            (yDiff == 2 || nodeDifferences(y).equals([2, 2]))
        ) {
            parent.demote();
            this.record("Propagating error by demoting parent", parent);

            if (yDiff != 2) {
                y.demote();
                this.record("Demoting y", y);
            }

            x = parent;
            parent = x.parent;
            if (!parent) {
                return;
            }

            y = parent.left === x ? parent.right : parent.left;

            xDiff = nodeDifference(x, parent);
            yDiff = nodeDifference(y, parent);
        }

        if (!parent) {
            return;
        }

        let rotatingAroundRoot = parent.parent == null;

        let parentNodeDiffs = nodeDifferences(parent);
        if (parentNodeDiffs.sort().equals([1, 3])) {
            if (parent.left === x) {
                this.fixDelete(
                    x,
                    parent.right,
                    parent,
                    false,
                    rotatingAroundRoot,
                    rotateLeft,
                    rotateRight
                );
            } else {
                this.fixDelete(
                    x,
                    parent.left,
                    parent,
                    true,
                    rotatingAroundRoot,
                    rotateRight,
                    rotateLeft
                );
            }
        }
    }

    deleteFixup(y, parent) {
        if (nodeDifferences(y).equals([2, 2])) {
            y.demote();
            this.record(
                "Starting deletion rebalance by demoting (2, 2) node",
                y
            );

            parent = y.parent;
        } else if (nodeDifferences(parent).equals([2, 2])) {
            parent.demote();
            this.record(
                "Starting deletion rebalance by demoting (2, 2) node",
                parent
            );

            parent = parent.parent;
        }

        if (!parent) {
            return;
        }

        [parent.left, parent.right].forEach((y) => {
            if (nodeDifference(y, parent) == 3) {
                this.bottomUpDelete(y, parent);
            }
        });
    }

    deleteRebalance(node, parent) {
        this.deleteFixup(node, parent);
    }
}