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Add Tower of Hanoi.
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‎README.md‎

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* [Eulerian Path and Eulerian Circuit](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/graph/eulerian-path) - Fleury's algorithm
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* [Strongly Connected Components](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/graph/strongly-connected-components) - Kosaraju's algorithm
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* **Uncategorized**
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* [Tower of Hanoi](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/uncategorized/hanoi-tower)
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* Union-Find
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* Maze
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* Sudoku
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* [Prim’s Algorithm](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/graph/prim) - finding Minimum Spanning Tree (MST) for weighted undirected graph
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* [Kruskal’s Algorithm](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/graph/kruskal) - finding Minimum Spanning Tree (MST) for weighted undirected graph
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* **Divide and Conquer**
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* [Tower of Hanoi](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/uncategorized/hanoi-tower)
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* [Euclidean Algorithm](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/math/euclidean-algorithm) - calculate the Greatest Common Divisor (GCD)
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* [Permutations](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/sets/permutations) (with and without repetitions)
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* [Combinations](https://github.com/trekhleb/javascript-algorithms/tree/master/src/algorithms/sets/combinations) (with and without repetitions)
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# Tower of Hanoi
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The Tower of Hanoi (also called the Tower of Brahma or Lucas'
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Tower and sometimes pluralized) is a mathematical game or puzzle.
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It consists of three rods and a number of disks of different sizes,
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which can slide onto any rod. The puzzle starts with the disks in
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a neat stack in ascending order of size on one rod, the smallest
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at the top, thus making a conical shape.
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The objective of the puzzle is to move the entire stack to another
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rod, obeying the following simple rules:
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- Only one disk can be moved at a time.
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- Each move consists of taking the upper disk from one of the
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stacks and placing it on top of another stack or on an empty rod.
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- No disk may be placed on top of a smaller disk.
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![Hanoi Tower](https://upload.wikimedia.org/wikipedia/commons/8/8d/Iterative_algorithm_solving_a_6_disks_Tower_of_Hanoi.gif)
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Animation of an iterative algorithm solving 6-disk problem
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With `3` disks, the puzzle can be solved in `7` moves. The minimal
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number of moves required to solve a Tower of Hanoi puzzle
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is `2n − 1`, where `n` is the number of disks.
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## References
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- [Wikipedia](https://en.wikipedia.org/wiki/Tower_of_Hanoi)
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- [HackerEarth](https://www.hackerearth.com/blog/algorithms/tower-hanoi-recursion-game-algorithm-explained/)
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import hanoiTower from '../hanoiTower';
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describe('hanoiTower', () => {
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it('should solve tower of hanoi puzzle with 2 discs', () => {
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const moveCallbackMock = jest.fn();
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hanoiTower(2, moveCallbackMock);
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expect(moveCallbackMock).toHaveBeenCalledTimes(3);
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expect(moveCallbackMock.mock.calls[0][0]).toBe(1);
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expect(moveCallbackMock.mock.calls[0][1]).toEqual([1, 2]);
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expect(moveCallbackMock.mock.calls[0][2]).toEqual([]);
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expect(moveCallbackMock.mock.calls[1][0]).toBe(2);
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expect(moveCallbackMock.mock.calls[1][1]).toEqual([2]);
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expect(moveCallbackMock.mock.calls[1][2]).toEqual([]);
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expect(moveCallbackMock.mock.calls[2][0]).toBe(1);
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expect(moveCallbackMock.mock.calls[2][1]).toEqual([1]);
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expect(moveCallbackMock.mock.calls[2][2]).toEqual([2]);
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});
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it('should solve tower of hanoi puzzle with 3 discs', () => {
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const moveCallbackMock = jest.fn();
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hanoiTower(3, moveCallbackMock);
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expect(moveCallbackMock).toHaveBeenCalledTimes(7);
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});
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it('should solve tower of hanoi puzzle with 6 discs', () => {
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const moveCallbackMock = jest.fn();
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hanoiTower(6, moveCallbackMock);
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expect(moveCallbackMock).toHaveBeenCalledTimes(63);
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});
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});
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import Stack from '../../../data-structures/stack/Stack';
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/**
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* @param {Stack} fromPole
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* @param {Stack} toPole
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* @param {function(disc: number, fromPole: number[], toPole: number[])} moveCallback
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*/
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function moveDisc(fromPole, toPole, moveCallback) {
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moveCallback(fromPole.peek(), fromPole.toArray(), toPole.toArray());
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const disc = fromPole.pop();
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toPole.push(disc);
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}
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/**
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* @param {number} numberOfDiscs
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* @param {Stack} fromPole
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* @param {Stack} withPole
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* @param {Stack} toPole
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* @param {function(disc: number, fromPole: number[], toPole: number[])} moveCallback
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*/
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function hanoiTowerRecursive({
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numberOfDiscs,
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fromPole,
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withPole,
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toPole,
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moveCallback,
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}) {
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if (numberOfDiscs === 1) {
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// Base case with just one disc.
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moveDisc(fromPole, toPole, moveCallback);
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} else {
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// In case if there are more discs then move them recursively.
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// Expose the bottom disc on fromPole stack.
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hanoiTowerRecursive({
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numberOfDiscs: numberOfDiscs - 1,
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fromPole,
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withPole: toPole,
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toPole: withPole,
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moveCallback,
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});
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// Move the disc that was exposed to its final destination.
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hanoiTowerRecursive({
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numberOfDiscs: 1,
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fromPole,
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withPole,
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toPole,
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moveCallback,
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});
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// Move temporary tower from auxiliary pole to its final destination.
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hanoiTowerRecursive({
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numberOfDiscs: numberOfDiscs - 1,
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fromPole: withPole,
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withPole: fromPole,
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toPole,
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moveCallback,
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});
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}
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}
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/**
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* @param {number} numberOfDiscs
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* @param {function(disc: number, fromPole: number[], toPole: number[])} moveCallback
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*/
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export default function hanoiTower(numberOfDiscs, moveCallback) {
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// Each of three poles of Tower of Hanoi puzzle is represented as a stack
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// that might contain elements (discs). Each disc is represented as a number.
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// Larger discs have bigger number equivalent.
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// The pole from where the discs should be moved.
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const fromPole = new Stack();
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// The middle pole that should be used as a helper.
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const withPole = new Stack();
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// The destination pole where all discs need to be moved.
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const toPole = new Stack();
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// Let's create the discs and put them to the fromPole.
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for (let discSize = numberOfDiscs; discSize > 0; discSize -= 1) {
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fromPole.push(discSize);
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}
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hanoiTowerRecursive({
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numberOfDiscs,
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fromPole,
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withPole,
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toPole,
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moveCallback,
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});
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}

‎src/data-structures/stack/Stack.js‎

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}
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/**
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* @return {LinkedListNode}
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* @return {*}
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*/
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peek() {
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if (!this.linkedList.tail) {

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