Added hard/nim_winner

bradhanson · bradhanson · commit 2e89f9055be0 · 2018-07-16T15:40:33.000-04:00
diff --git a/hard/nim_winner.js b/hard/nim_winner.js
@@ -0,0 +1,27 @@
+/**
+ * Using the JavaScript language, have the function NimWinner(arr) take the
+ * array of integers stored in arr which will represent the amount of coins in
+ * each pile. For example: [2, 4, 1, 3] means there are 4 piles of coins and
+ * there are 2 coins in the first pile, 4 in the second pile, etc. Nim is played
+ * by each player removing any number of coins from only one pile, and the
+ * winner is the player who picks up the last coin. For example: if arr is [1,
+ * 2, 3] then for example player 1 can remove 2 coins from the last pile which
+ * results in [1, 2, 1]. Then player 2 can remove 1 coin from the first pile
+ * which results in [0, 2, 1], etc. The player that has the last possible move
+ * taking the last coin(s) from a pile wins the game. Your program should output
+ * either 1 or 2 which represents which player has a guaranteed win with perfect
+ * play for the Nim game.
+ *
+ * https://www.coderbyte.com/results/bhanson:Nim%20Winner:JavaScript
+ *
+ * @param  {array} arr
+ * @return {number}
+ */
+function nimWinner(arr) {
+    // https://en.wikipedia.org/wiki/Nim#Mathematical_theory
+    const nimSum = arr.reduce((nimSum, num) => nimSum ^ num);
+    const winningPlayer = nimSum === 0 ? 2 : 1;
+    return winningPlayer;
+}
+
+module.exports = nimWinner;
diff --git a/hard/nim_winner.test.js b/hard/nim_winner.test.js
@@ -0,0 +1,25 @@
+const nimWinner = require('./nim_winner');
+
+describe('nimWinner()', () => {
+    test('passes Coderbyte.com tests', () => {
+        expect(nimWinner([1, 2, 3])).toBe(2);
+
+        expect(nimWinner([1, 1, 1, 4, 5, 4])).toBe(1);
+
+        expect(nimWinner([1, 1, 1, 1])).toBe(2);
+
+        expect(nimWinner([1, 1, 1])).toBe(1);
+
+        expect(nimWinner([1, 2, 3, 4])).toBe(1);
+
+        expect(nimWinner([1, 2, 3, 4, 5, 6])).toBe(1);
+
+        expect(nimWinner([1, 2, 3, 4, 5, 6, 7])).toBe(2);
+
+        expect(nimWinner([3, 3, 3, 3])).toBe(2);
+
+        expect(nimWinner([5, 1, 2, 4, 2])).toBe(2);
+
+        expect(nimWinner([5, 5, 1, 4, 4])).toBe(1);
+    });
+});
