Added hard/matching_couples

bradhanson · bradhanson · commit fea5955829db · 2018-07-16T11:47:15.000-04:00
diff --git a/hard/matching_couples.js b/hard/matching_couples.js
@@ -0,0 +1,48 @@
+/**
+ * Using the JavaScript language, have the function matchingCouples(arr) take
+ * the arr parameter being passed which will be an array of integers in the
+ * following format: [B, G, N] where B represents the number of boys, G
+ * represents the number of girls, and N represents how many people you want to
+ * pair together. Your program should return the number of different ways you
+ * can match boys with girls given the different arguments. For example: if arr
+ * is [5, 3, 2], N=2 here so you want to pair together 2 people, so you'll need
+ * 1 boy and 1 girl. You have 5 ways to choose a boy and 3 ways to choose a
+ * girl, so your program should return 15. Another example: if arr is [10, 5,
+ * 4], here N=4 so you need 2 boys and 2 girls. We can choose 2 boys from a
+ * possible 10, and we can choose 2 girls from a possible 5. Then we have 2
+ * different ways to pair the chosen boys and girls. Our program should
+ * therefore return 900
+ *
+ * N will always be an even number and it will never be greater than the maximum
+ * of (B, G). B and G will always be greater than zero.
+ *
+ * https://www.coderbyte.com/results/bhanson:Matching%20Couples:JavaScript
+ *
+ * @param  {array} arr
+ * @return {number}
+ */
+function matchingCouples(arr) {
+    const [boys, girls, numPairs] = arr;
+
+    const numEachGender = numPairs / 2;
+
+    const boyCombos = choose(boys, numEachGender);
+    const girlCombos = choose(girls, numEachGender);
+    const totalCombos = boyCombos * girlCombos * factorial(numEachGender);
+
+    return totalCombos;
+}
+
+function factorial(num) {
+    let sum = 1;
+    for (let i = 1; i <= num; i++) {
+        sum *= i;
+    }
+    return sum;
+}
+
+function choose(num, k) {
+    return factorial(num) / (factorial(k) * factorial(num - k));
+}
+
+module.exports = matchingCouples;
diff --git a/hard/matching_couples.test.js b/hard/matching_couples.test.js
@@ -0,0 +1,25 @@
+const matchingCouples = require('./matching_couples');
+
+describe('matchingCouples()', () => {
+    test('passes Coderbyte.com tests', () => {
+        expect(matchingCouples([5, 3, 2])).toBe(15);
+
+        expect(matchingCouples([10, 5, 4])).toBe(900);
+
+        expect(matchingCouples([5, 5, 4])).toBe(200);
+
+        expect(matchingCouples([2, 2, 2])).toBe(4);
+
+        expect(matchingCouples([10, 10, 4])).toBe(4050);
+
+        expect(matchingCouples([5, 5, 2])).toBe(25);
+
+        expect(matchingCouples([10, 10, 6])).toBe(86400);
+
+        expect(matchingCouples([6, 6, 4])).toBe(450);
+
+        expect(matchingCouples([10, 5, 4])).toBe(900);
+
+        expect(matchingCouples([15, 10, 6])).toBe(327600);
+    });
+});
