From 2c885d5f8027123e8c4b155156d2b9877f40c9c7 Mon Sep 17 00:00:00 2001
From: HamsterCoder <sirinity13@gmail.com>
Date: Mon, 4 Dec 2023 16:44:01 +0100
Subject: [PATCH] Code basic BST. Add some tests.

---
 README.md                    |   6 ++
 src/BinarySearchTree.test.ts |  61 ++++++++++++++++++
 src/BinarySearchTree.ts      | 122 +++++++++++++++++++++++++++++++++++
 tsconfig.json                |   2 +-
 4 files changed, 190 insertions(+), 1 deletion(-)
 create mode 100644 src/BinarySearchTree.test.ts
 create mode 100644 src/BinarySearchTree.ts

diff --git a/README.md b/README.md
index 9299c13..703d329 100644
--- a/README.md
+++ b/README.md
@@ -4,12 +4,18 @@ This repository contains implementations of some data structures and algorithms.
 
 ### What do you have?
 
+#### Sorts and shuffles
+
 * Knuth Shuffle - returns a shuffled copy of the array
 * Shell Sort - returns a sorted copy of the array
 * Quick Sort - returns a sorted copy of the array
 * Insertion Sort - returns a sorted copy of the array
+
+#### Data structures
 * MaxHeap - allows for `add` and `removeMax` operations (with heapify)
 * MinHeap - allows for `add` and `removeMin` operations (with heapify)
+* Heap - allows for `add` and `removeRoot` operations (with heapify)
+* BinarySearchTree - allows for `set`, `get`, `min`, `max`, iteration (no deletion)
 
 ## Development
 
diff --git a/src/BinarySearchTree.test.ts b/src/BinarySearchTree.test.ts
new file mode 100644
index 0000000..8e5b0fe
--- /dev/null
+++ b/src/BinarySearchTree.test.ts
@@ -0,0 +1,61 @@
+import { BinarySearchTree } from "./BinarySearchTree";
+
+describe('BinarySearchTree', () => {
+    let bst: BinarySearchTree<string, number>;
+
+    beforeEach(() => {
+        bst = new BinarySearchTree((a, b) => a > b ? 1 : (a === b ? 0 : -1));
+    });
+
+    test('Sets and gets one key-value', () => {
+        bst.set('a', 0);
+        expect(bst.get('a')).toEqual(0);
+        expect(bst.root?.count).toEqual(1);
+    });
+
+    test('Sets and gets a pair of key-values', () => {
+        bst.set('a', 0);
+        bst.set('b', 1);
+
+        for (let node of bst) {
+            console.log(node?.key, node?.value);
+        }
+
+        expect(bst.get('a')).toEqual(0);
+        expect(bst.get('b')).toEqual(1);
+        expect(bst.root?.count).toEqual(2);
+    });
+
+    test('Provides in order iteration', () => {
+        bst.set('a', 0);
+        bst.set('b', 1);
+        bst.set('c', 2);
+        bst.set('d', 3);
+        bst.set('e', 4);
+        bst.set('f', 5);
+
+        expect(bst.root?.count).toEqual(6);
+
+        let prev;
+
+        for (let node of bst) {
+            if (!prev) {
+                prev = node;
+            } else {
+                expect(bst.compare(node?.key, prev?.key) === 1).toBeTruthy();
+            }
+        }
+    });
+
+    test('Returns min and max', () => {
+        bst.set('a', 0);
+        bst.set('b', 1);
+        bst.set('c', 2);
+        bst.set('d', 3);
+        bst.set('e', 4);
+        bst.set('f', 5);
+
+        expect(bst.min()?.key).toEqual('a');
+        expect(bst.max()?.key).toEqual('f');
+    });
+});
\ No newline at end of file
diff --git a/src/BinarySearchTree.ts b/src/BinarySearchTree.ts
new file mode 100644
index 0000000..c71e88b
--- /dev/null
+++ b/src/BinarySearchTree.ts
@@ -0,0 +1,122 @@
+export interface TreeNode<K, V> {
+  key: K;
+  value: V;
+  count: number;
+  left: TreeNode<K, V> | null;
+  right: TreeNode<K, V> | null;
+}
+
+// TODO
+// Add this method description to docs
+// Rank: how many keys are smaller than k, bigger than k
+
+export class BinarySearchTree<K, V> {
+  root: TreeNode<K, V> | null = null;
+  compare: (a: K, b: K) => number;
+
+  constructor(compare: (a: K, b: K) => number) {
+    this.compare = compare;
+  }
+
+  [Symbol.iterator](this: BinarySearchTree<K, V>): Iterator<TreeNode<K, V>> {
+    const items = this.getSortedNodes(this.root);
+    let i = 0;
+    return {
+        next() {
+            if (i === items.length) {
+                return { done: true, value: undefined };
+            }
+
+            return { value: items[i++]};
+        }
+    };
+  }
+
+  private getSortedNodes(node: TreeNode<K, V> | null): TreeNode<K, V>[] {
+    if (node === null) {
+        return [];
+    }
+
+    return [
+        ...this.getSortedNodes(node.left),
+        node,
+        ...this.getSortedNodes(node.right)
+    ];
+  }
+
+  get(key: K): V | null {
+    let root = this.root;
+
+    while (root !== null) {
+      let cmp = this.compare(key, root.key);
+
+      if (cmp < 0) {
+        root = root.left;
+      } else if (cmp > 0) {
+        root = root.right;
+      } else {
+        return root.value;
+      }
+    }
+
+    return null;
+  }
+
+  size(node: TreeNode<K, V> | null): number {
+    if (node === null) {
+      return 0;
+    }
+
+    return node.count;
+  }
+
+  private _set(node: TreeNode<K, V> | null, key: K, value: V): TreeNode<K, V> {
+    if (node === null) {
+      return {
+        key,
+        value,
+        count: 1,
+        left: null,
+        right: null,
+      };
+    }
+
+    let cmp = this.compare(key, node.key);
+
+    if (cmp < 0) {
+      node.left = this._set(node.left, key, value);
+    } else if (cmp > 0) {
+      node.right = this._set(node.right, key, value);
+    } else {
+      node.value = value;
+    }
+
+    node.count = 1 + this.size(node.left) + this.size(node.right);
+
+    return node;
+  }
+
+  set(key: K, value: V): void {
+    this.root = this._set(this.root, key, value);
+  }
+
+  min(): TreeNode<K, V> | null {
+    let node = this.root;
+
+    while (node?.left) {
+        node = node.left;
+    }
+
+    return node;
+  }
+
+  max(): TreeNode<K, V> | null {
+    let node = this.root;
+
+    while (node?.right) {
+        node = node.right;
+    }
+
+    return node;
+  }
+}
diff --git a/tsconfig.json b/tsconfig.json
index 258070b..fe0756d 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -1,6 +1,6 @@
 {
     "compilerOptions": {
-      "target": "ES5",
+      "target": "es2015",
       "module": "CommonJS",
       "rootDir": "src",
       "outDir": "dist",