Add BinaryHeap, Memo, and StateMachine, fixup previous caught bugs

tools/structures/Stack.ts

@@ -0,0 +1,43 @@
+/**
+ * Data structure allowing for the insertion and removal of
+ * elements in a LIFO manner in `O(1)` time.
+ * @author MindfulMinun
+ * @since 2022-10-22
+ */
+export class Stack<T> implements Iterable<T> {
+    #elements: Record<number, T>
+    #head: number
+
+    constructor(initials?: Iterable<T>) {
+        this.#elements = {}
+        this.#head = 0
+        if (!initials) return
+        for (const el of initials) this.push(el)
+    }
+
+    /** Add an element to the stack */
+    push(element: T): void {
+        this.#elements[this.#head++] = element
+    }
+
+    /** Remove an element from the stack and return it. */
+    pop(): T | undefined {
+        if (this.length === 0) return undefined
+        const el = this.#elements[--this.#head]
+        delete this.#elements[this.#head]
+        return el
+    }
+
+    /** Preview the topmost element of the stack without removing it. */
+    peek(): T | undefined {
+        if (this.length === 0) return undefined
+        return this.#elements[this.#head - 1]
+    }
+
+    /** The number of elements remaining in the stack */
+    get length() { return this.#head }
+
+    *[Symbol.iterator]() {
+        while (this.length !== 0) yield this.pop()!
+    }
+}