💥 refactor!: Simplify swap functions.

BREAKING CHANGE: These functions are not as generic anymore.

Author: make-github-pseudonymous-again

src/swap/swap_left.js

@@ -4,15 +4,18 @@ import replace_node from '../deletion/replace_node.js';
 import swap_color from './swap_color.js';
 
 /**
- * Swap pointers and colors of a node and its left child.
+ * Swap pointers and colors of a node and its left child B with one constraint:
+ *   - B's right child is a leaf
+ *
+ * NOTE: This constraint is implied because B is A's in-subtree predecessor.
  *
  *         p                   p
  *         |                   |
  *        -A                  -B
  *        / \                 / \
  *      +B   c       ->     +A   c
  *      / \                 / \
- *     a   b               a   b
+ *     a   -               a   -
  *
  * @param {Node} A - The node.
  * @return {Node} The node B.
@@ -23,7 +26,7 @@ const swap_left = (A) => {
 	const B = A.left;
 	assert(B instanceof Node);
 	const a = B.left;
-	const b = B.right;
+	assert(B.right === null);
 	const c = A.right;
 
 	if (A.parent === null) {
@@ -34,8 +37,7 @@ const swap_left = (A) => {
 
 	A.parent = B;
 
-	A.right = b;
-	if (b !== null) b.parent = A;
+	A.right = null;
 	B.right = c;
 	if (c !== null) c.parent = B;
 

src/swap/swap_non_adjacent.js

@@ -3,13 +3,19 @@ import Node from '../types/Node.js';
 import swap_color from './swap_color.js';
 
 /**
- * Swap pointers and colors of two NON-ADJACENT nodes.
+ * Swap pointers and colors of two NON-ADJACENT nodes with three constraints:
+ *   - B is not the root
+ *   - B is its parent right child
+ *   - B's right child is a leaf
  *
- *         p         q             q         p
- *         |         |             |         |
+ * NOTE: These three constraints are implied because B is A's in-subtree
+ * predecessor without being A's left child.
+ *
+ *         p       q             q           p
+ *         |        \             \          |
  *        -A        +B            +A        -B
  *        / \       / \           / \       / \
- *       u   v     x   y     ->  x   y     u   v
+ *       u   v     x   -     ->  x   -     u   v
  *
  * @param {Node} A - The first node.
  * @param {Node} B - The second node.
@@ -23,27 +29,25 @@ const swap_non_adjacent = (A, B) => {
 	const v = A.right;
 	const q = B.parent;
 	const x = B.left;
-	const y = B.right;
+	assert(B.right === null);
+	assert(q !== null);
+	assert(B === q.right);
 
 	if (p !== null) {
 		if (A === p.left) p.left = B;
 		else p.right = B;
 	}
 
-	if (q !== null) {
-		if (B === q.right) q.right = A;
-		else q.left = A;
-	}
+	q.right = A;
 
 	A.parent = q;
 	A.left = x;
-	A.right = y;
+	A.right = null;
 	B.parent = p;
 	B.left = u;
 	B.right = v;
 
 	if (x !== null) x.parent = A;
-	if (y !== null) y.parent = A;
 	if (u !== null) u.parent = B;
 	if (v !== null) v.parent = B;