Added hard/array_couples

bradhanson · bradhanson · commit 06d08a4fa94e · 2018-07-10T21:19:15.000-04:00
diff --git a/hard/array_couples.js b/hard/array_couples.js
@@ -0,0 +1,48 @@
+/**
+ * Using the JavaScript language, have the function arrayCouples(arr) take the
+ * arr parameter being passed which will be an array of an even number of
+ * positive integers, and determine if each pair of integers, [k, k+1], [k+2,
+ * k+3], etc. in the array has a corresponding reversed pair somewhere else in
+ * the array. For example: if arr is [4, 5, 1, 4, 5, 4, 4, 1] then your program
+ * should output the string yes because the first pair 4, 5 has the reversed
+ * pair 5, 4 in the array, and the next pair, 1, 4 has the reversed pair 4, 1 in
+ * the array as well. But if the array doesn't contain all pairs with their
+ * reversed pairs, then your program should output a string of the integer pairs
+ * that are incorrect, in the order that they appear in the array.
+ *
+ * For example: if arr is [6, 2, 2, 6, 5, 14, 14, 1] then your program should
+ * output the string 5,14,14,1 with only a comma separating the integers.
+ * @param  {array} arr
+ * @return {string}
+ */
+function arrayCouples(arr) {
+    const unmatchedPairs = [];
+    for (let i = 0; i < arr.length; i += 2) {
+        let left = arr[i];
+        let right = arr[i + 1];
+        if (!pairInArray(arr, [right, left], i)) {
+            unmatchedPairs.push([left, right]);
+        }
+    }
+    return unmatchedPairs.length === 0 ? 'yes' : unmatchedPairs.join(',');
+}
+
+/**
+ * Iterates over array of numbers by index delta of 2 and checks for a pair of
+ * numbers
+ * @param  {array} arr array of numbers
+ * @param  {array} pair array of length 2, a pair of numbers
+ * @param  {number} excludeIndex an even numbered index to skip
+ * @return {boolean}
+ */
+function pairInArray(arr, pair, excludeIndex) {
+    let [left, right] = pair;
+    for (let i = 0; i < arr.length; i += 2) {
+        if (excludeIndex !== i && arr[i] === left && arr[i + 1] === right) {
+            return true;
+        }
+    }
+    return false;
+}
+
+module.exports = arrayCouples;
diff --git a/hard/array_couples.test.js b/hard/array_couples.test.js
@@ -0,0 +1,13 @@
+const arrayCouples = require('./array_couples');
+
+describe('arrayCouples()', () => {
+    test('correctly returns string true for matching pairs', () => {
+        expect(arrayCouples([4, 5, 1, 4, 5, 4, 4, 1])).toBe('yes');
+        expect(arrayCouples([5, 4, 6, 7, 7, 6, 4, 5])).toBe('yes');
+    });
+
+    test('correctly returns string of unmatched pairs', () => {
+        expect(arrayCouples([6, 2, 2, 6, 5, 14, 14, 1])).toBe('5,14,14,1');
+        expect(arrayCouples([2, 1, 1, 2, 3, 3])).toBe('3,3');
+    });
+});
