Remove usage of explicit leaves

mangle.json

@@ -2,14 +2,13 @@
   "minify": {
     "mangle": {
       "properties": {
-        "regex": "^(_color|isLeaf)$"
+        "regex": "^_color$"
       }
     }
   },
   "props": {
     "props": {
-      "$_color": "c",
-      "$isLeaf": "L"
+      "$_color": "c"
     }
   }
 }

package.json

@@ -42,7 +42,7 @@
     "build-gh-pages": "npm run build-docs",
     "ci:test": "npm run lint-config && npm run lint && npm run cover",
     "commit-msg": "commitlint --edit",
-    "cover": "c8 --all --src src --reporter=lcov npm test",
+    "cover": "NODE_ENV=cover c8 --all --src src --reporter=lcov npm test",
     "debug": "NODE_ENV=debug npm run test -- -st --fail-fast",
     "dev": "npm run lint-config-and-fix && npm run lint-and-fix && npm run cover -- -- -st --fail-fast",
     "install-hooks": "husky install",
@@ -104,40 +104,33 @@
       [
         "@babel/preset-env",
         {
-          "targets": [
-            "defaults",
-            "maintained node versions"
+          "targets": "current node"
+        }
+      ]
+    ],
+    "plugins": [
+      [
+        "transform-remove-console",
+        {
+          "exclude": [
+            "log",
+            "error",
+            "warn"
           ]
         }
       ]
     ],
     "env": {
       "debug": {
         "presets": [
-          [
-            "@babel/preset-env",
-            {
-              "targets": "current node"
-            }
-          ],
-          "babel-preset-power-assert"
-        ]
-      },
-      "test": {
-        "presets": [
-          [
-            "@babel/preset-env",
-            {
-              "targets": "current node"
-            }
-          ],
           "babel-preset-power-assert"
         ],
         "plugins": [
           [
             "transform-remove-console",
             {
               "exclude": [
+                "debug",
                 "log",
                 "error",
                 "warn"
@@ -146,36 +139,45 @@
           ]
         ]
       },
-      "development": {
+      "test": {
         "presets": [
           "babel-preset-power-assert"
-        ],
-        "plugins": [
+        ]
+      },
+      "cover": {
+        "sourceMaps": "inline",
+        "presets": [
+          "babel-preset-power-assert"
+        ]
+      },
+      "development": {
+        "presets": [
           [
-            "transform-remove-console",
+            "@babel/preset-env",
             {
-              "exclude": [
-                "log",
-                "error",
-                "warn"
+              "targets": [
+                "defaults",
+                "maintained node versions"
               ]
             }
-          ]
+          ],
+          "babel-preset-power-assert"
         ]
       },
       "production": {
-        "plugins": [
-          "babel-plugin-unassert",
+        "presets": [
           [
-            "transform-remove-console",
+            "@babel/preset-env",
             {
-              "exclude": [
-                "log",
-                "error",
-                "warn"
+              "targets": [
+                "defaults",
+                "maintained node versions"
               ]
             }
           ]
+        ],
+        "plugins": [
+          "babel-plugin-unassert"
         ]
       }
     }

src/debug/_debug.js

@@ -1,6 +1,5 @@
 import assert from 'assert';
 import Node from '../types/Node.js';
-import Leaf from '../types/Leaf.js';
 import BLACK from '../color/BLACK.js';
 
 /**
@@ -14,15 +13,11 @@ const _debug = ({red, black}) => {
 	 * Recursively constructs a prettyprint string for the red-black tree rooted at
 	 * <code>root</code>.
 	 *
-	 * @param {Node|Leaf} root - The root of the tree.
+	 * @param {Node} root - The root of the tree.
 	 * @returns {string}
 	 */
 	const debug = (root) => {
-		assert(root instanceof Node || root instanceof Leaf);
-		if (root.isLeaf()) {
-			assert(root instanceof Leaf);
-			return black('L');
-		}
+		if (root === null) return black('L');
 
 		assert(root instanceof Node);
 

src/deletion/delete_case0.js

@@ -0,0 +1,23 @@
+import assert from 'assert';
+import BLACK from '../color/BLACK.js';
+import Node from '../types/Node.js';
+import delete_case1 from './delete_case1.js';
+
+/**
+ * Preconditions:
+ *   - n is black
+ *   - all root-leaf paths going through n have a black height of b - 1
+ *   - all other root-leaf paths have a black height of b
+ *
+ * @param {Node} n - The input node.
+ */
+const delete_case0 = (n) => {
+	assert(n instanceof Node);
+	assert(n._color === BLACK);
+	// If n is the root, there is nothing to do:
+	//   - all paths go through n, and
+	//   - n is black.
+	if (n.parent !== null) delete_case1(n);
+};
+
+export default delete_case0;

src/deletion/delete_case1.js

@@ -1,24 +1,52 @@
 import assert from 'assert';
 import BLACK from '../color/BLACK.js';
+import RED from '../color/RED.js';
 import Node from '../types/Node.js';
-import Leaf from '../types/Leaf.js';
+import rotate_left from '../rotate/rotate_left.js';
+import rotate_right from '../rotate/rotate_right.js';
+import sibling from '../family/sibling.js';
+
 import delete_case2 from './delete_case2.js';
+import delete_case3 from './delete_case3.js';
 
 /**
  * Preconditions:
  *   - n is black
  *   - all root-leaf paths going through n have a black height of b - 1
  *   - all other root-leaf paths have a black height of b
+ *   - n is not the root
  *
- * @param {Node|Leaf} n - The input node.
+ * @param {Node} n - The input node.
  */
 const delete_case1 = (n) => {
-	assert(n instanceof Node || n instanceof Leaf);
+	assert(n instanceof Node);
 	assert(n._color === BLACK);
-	// If n is the root, there is nothing to do:
-	//   - all paths go through n, and
-	//   - n is black.
-	if (n.parent !== null) delete_case2(n);
+	assert(n.parent !== null);
+
+	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) {
+		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_case2.js

@@ -2,50 +2,52 @@ import assert from 'assert';
 import BLACK from '../color/BLACK.js';
 import RED from '../color/RED.js';
 import Node from '../types/Node.js';
-import Leaf from '../types/Leaf.js';
-import rotate_left from '../rotate/rotate_left.js';
-import rotate_right from '../rotate/rotate_right.js';
 import sibling from '../family/sibling.js';
 
+import delete_case0 from './delete_case0.js';
 import delete_case3 from './delete_case3.js';
-import delete_case4 from './delete_case4.js';
 
 /**
  * Preconditions:
  *   - n is black
  *   - all root-leaf paths going through n have a black height of b - 1
  *   - all other root-leaf paths have a black height of b
  *   - n is not the root
+ *   - n's sibling is black
  *
- * @param {Node|Leaf} n - The input node.
+ * @param {Node} n - The input node.
  */
 const delete_case2 = (n) => {
-	assert(n instanceof Node || n instanceof Leaf);
+	assert(n instanceof Node);
 	assert(n._color === BLACK);
 	assert(n.parent !== null);
-
 	const s = sibling(n);
+	assert(s instanceof Node);
+	assert(s._color === BLACK);
 
 	/**
-	 * If n's sibling is red, prepare for and go to case 4.
+	 * If n's parent is black and n's sibling's children are black, then
+	 * repaint n's sibling red. Now all root-leaf paths going through n's
+	 * parent have a black height of b - 1. We recurse thus on n's parent.
 	 *
-	 *           B                       B
+	 *           B                      >B
 	 *         /   \                  /     \
-	 *      >B       R               R       B
-	 *      / \     / \     -->    /   \    / \
-	 *     -   -  B     B        >B     B  =   =
-	 *           / \   / \       / \   / \
-	 *          =   = =   =     -   - =   =
+	 *      >B       B               B       R
+	 *      / \     / \     -->     / \     / \
+	 *     -   -  B     B          -   -  B     B
+	 *           / \   / \               / \   / \
+	 *          -   - -   -             -   - -   -
 	 */
-	if (s._color === RED) {
-		n.parent._color = RED;
-		s._color = BLACK;
-		if (n === n.parent.left) rotate_left(n.parent);
-		else rotate_right(n.parent);
-		delete_case4(n);
+	if (
+		n.parent._color === BLACK &&
+		(s.left === null || s.left._color === BLACK) &&
+		(s.right === null || s.right._color === BLACK)
+	) {
+		s._color = RED;
+		delete_case0(n.parent);
 	}
 
-	// Otherwise, go to case 3.
+	// Otherwise, go to case 4.
 	else delete_case3(n);
 };