JS solution and test for DCP #2

Author: womcauliff

Daily-Coding-Problem/2-Product-of-All-Others/README.md

@@ -0,0 +1,14 @@
+# Problem #2 [Hard]
+
+## Problem Description
+
+> Given an array of integers, return a new array such that each element at index `i` of the new array is the product of all the numbers in the original array except the one at `i`.
+
+## Implementation
+
+My solution generates the result array by sweeping through the source array twice, which means it falls under time complexity of `O(n)`, where `n` is the number of elements in the source array.
+
+- JavaScript
+  - [Solution](./productOfAllOthers.js)
+  - [Jest Test File](./productOfAllOthers.test.js)
+  - [CodeSandbox](https://codesandbox.io/s/586mk36lx?autoresize=1&fontsize=14&module=%2FproductOfAllOthers.js&previewwindow=tests)

Daily-Coding-Problem/2-Product-of-All-Others/productOfAllOthers.js

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+/**
+ * Given an array of integers, returns a new array such that each element at index i
+ * of the new array is the product of all the numbers in the original array
+ * except the one at i.
+ * @param {Number[]} arr An array of integers.
+ * @return {Number[]} The resulting array.
+ */
+function productOfAllOthers(arr) {
+  // Reduce the elements of source array into the total product of all elements
+  const totalProduct = arr.reduce(
+    (runningProduct, currentVal) => (runningProduct *= currentVal),
+    1
+  );
+
+  // Map over the source array to return a result array where each
+  // resulting element is the totalProduct divided by the original element.
+  return arr.map(num => totalProduct / num);
+}
+
+// Naive brute-force approach
+function bruteForceProductOfAllOthers(arr) {
+  const result = [];
+  for (let i = 0; i < arr.length; i++) {
+    let product = 1;
+    for (let j = 0; j < arr.length; j++) {
+      if (arr[j] !== arr[i]) {
+        product *= arr[j];
+      }
+    }
+    result.push(product);
+  }
+  return result;
+}
+
+export default productOfAllOthers;

Daily-Coding-Problem/2-Product-of-All-Others/productOfAllOthers.test.js

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+import productOfAllOthers from "./productOfAllOthers";
+
+test(`[1, 2, 3, 4, 5] returns [120, 60, 40, 30, 24]`, () => {
+  expect(productOfAllOthers([1, 2, 3, 4, 5])).toEqual([120, 60, 40, 30, 24]);
+});
+
+test(`[3, 2, 1] returns [2, 3, 6]`, () => {
+  expect(productOfAllOthers([3, 2, 1])).toEqual([2, 3, 6]);
+});

Daily-Coding-Problem/README.md

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+# Daily Coding Problem
+
+Solutions to problems received from [dailycodingproblem.com](https://www.dailycodingproblem.com)
+
+- [2. Product of All Others](./2-Product-of-All-Others/README.md)

README.md

@@ -69,3 +69,7 @@ The following problems are introduced in the [Interview Cake full course](https:
 - [42. Find Duplicate Files](./42-Find-Duplicate-Files/README.md)
 
 - [43. Merge Sorted Arrays](./43-Merge-Sorted-Arrays/README.md)
+
+## Daily Coding Problem
+
+- [2. Product of All Others](./Daily-Coding-Problem/2-Product-of-All-Others/README.md)