Added the king's tour problem (without solution)

Author: Murillo2380

src/hard-google-king-tour/README.md

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+# Description
+
+Good morning! Here's your coding interview problem for today.
+
+This problem was asked by **Google**.
+
+A knight's tour is a sequence of moves by a knight on a chessboard such that all squares are visited once.
+
+Given `N`, write a function to return the number of knight's tours on an `N` by `N` chessboard.
+
+# Source
+
+Received by email from the [Daily Coding Problem](https://www.dailycodingproblem.com)

src/hard-google-king-tour/js/Idea.md

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+# Idea behind the solution

src/hard-google-king-tour/js/solution.js

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+"use strict";
+// TODO BE IMPLEMENTED
+
+function isValid(i, j, n, visited) {
+    return i >= 0 && j >= 0 && i < n && j < n && !visited[i][j];
+}
+
+/**
+ *
+ * @param {Pos} currentPosition
+ * @param {number} n
+ * @param {boolean[][]} visited
+ */
+function solve(i, j, n, visited = new Array(n).fill(new Array(n))) {
+    let hasEnded = true;
+
+    if (!isValid(i, j, n, visited)) return 0;
+
+    visited[i][j] = true;
+    visited.forEach(row => {
+        if (row.some(val => val === false)) hasEnded = false;
+    });
+
+    if (hasEnded) return 1;
+
+    const possibilities = [];
+    possibilities.push(solve(i + 1, j, n, visited.map(arr => arr.slice())));
+    possibilities.push(solve(i - 1, j, n, visited.map(arr => arr.slice())));
+    possibilities.push(solve(i, j + 1, n, visited.map(arr => arr.slice())));
+    possibilities.push(solve(i, j - 1, n, visited.map(arr => arr.slice())));
+
+    return possibilities.reduce((total, current) => (total += current), 0);
+}
+
+console.log(solve(0, 0, 4));