♻️ refactor: Compare to 0 when possible.

This fixes #106.

Author: make-github-pseudonymous-again

src/deletion/delete_case1.js

@@ -26,27 +26,27 @@ const delete_case1 = (n) => {
 	const s = sibling(n);
 	assert(s instanceof Node);
 
-	/**
-	 * If n's sibling is red, prepare for and go to case 4.
-	 *
-	 *           B                       B
-	 *         /   \                  /     \
-	 *      >B       R               R       B
-	 *      / \     / \     -->    /   \    / \
-	 *     -   -  B     B        >B     B  =   =
-	 *           / \   / \       / \   / \
-	 *          =   = =   =     -   - =   =
-	 */
-	if (s._color === RED) {
+	if (s._color === BLACK) {
+		// If n's sibling is BLACK, go to case 3.
+		delete_case2(n);
+	} else {
+		/**
+		 * Otherwise, prepare for and go to case 4.
+		 *
+		 *           B                       B
+		 *         /   \                  /     \
+		 *      >B       R               R       B
+		 *      / \     / \     -->    /   \    / \
+		 *     -   -  B     B        >B     B  =   =
+		 *           / \   / \       / \   / \
+		 *          =   = =   =     -   - =   =
+		 */
 		n.parent._color = RED;
 		s._color = BLACK;
 		if (n === n.parent.left) rotate_left(n.parent);
 		else rotate_right(n.parent);
 		delete_case3(n);
 	}
-
-	// Otherwise, go to case 3.
-	else delete_case2(n);
 };
 
 export default delete_case1;

src/deletion/delete_case3.js

@@ -46,7 +46,7 @@ const delete_case3 = (n) => {
 	 */
 	if (
 		// The parent color test is always true when coming from case 2
-		n.parent._color === RED &&
+		n.parent._color !== BLACK &&
 		(s.left === null || s.left._color === BLACK) &&
 		(s.right === null || s.right._color === BLACK)
 	) {

src/deletion/delete_no_child.js

@@ -23,13 +23,12 @@ const delete_no_child = (n) => {
 	assert(n.left === null);
 	assert(n.right === null);
 
-	if (n._color === RED) {
+	if (n._color !== BLACK) {
+		assert(n._color === RED);
 		prune(n);
 		return;
 	}
 
-	assert(n._color === BLACK);
-
 	// Mock leaf since there is no left child
 	// We use key = n.key to avoid mixing types, but this property is never
 	// accessed.

src/insertion/insert_case2.js

@@ -39,7 +39,8 @@ const insert_case2 = (n) => {
 	 *     -   -                 -   -
 	 */
 
-	if (u !== null && u._color === RED) {
+	if (u !== null && u._color !== BLACK) {
+		assert(u._color === RED);
 		n.parent._color = BLACK;
 		u._color = BLACK;
 		const g = grandparent(n);