fix: fixed error in the MaxProductOfThree algorithm (TheAlgorithms#1295)

* fix: fixed error in the MaxProductOfThree algorithm Fixed the error in the MaxProductOfThree by initializing the max and min variables to null instead of -1. The checks were then altered to check for null instead of -1. Also wrote more tests, which randomly generated small arrays and compared the output of the maxProductOfThree-algorithm to the output of a slower, but complete, function which calculates all posible triple-products of the values of the array. Fixes: TheAlgorithms#1294 * fix: Added newlines at the end of the files

Author: Xolvez

Dynamic-Programming/MaxProductOfThree.js

@@ -10,25 +10,25 @@ export function maxProductOfThree (arrayItems) {
  const n = arrayItems.length
  if (n < 3) throw new Error('Triplet cannot exist with the given array')
  let max1 = arrayItems[0]
- let max2 = -1
- let max3 = -1
+ let max2 = null
+ let max3 = null
  let min1 = arrayItems[0]
- let min2 = -1
+ let min2 = null
  for (let i = 1; i < n; i++) {
  if (arrayItems[i] > max1) {
  max3 = max2
  max2 = max1
  max1 = arrayItems[i]
- } else if (max2 === -1 || arrayItems[i] > max2) {
+ } else if (max2 === null || arrayItems[i] > max2) {
  max3 = max2
  max2 = arrayItems[i]
- } else if (max3 === -1 || arrayItems[i] > max3) {
+ } else if (max3 === null || arrayItems[i] > max3) {
  max3 = arrayItems[i]
  }
  if (arrayItems[i] < min1) {
  min2 = min1
  min1 = arrayItems[i]
- } else if (min2 === -1 || arrayItems[i] < min2) {
+ } else if (min2 === null || arrayItems[i] < min2) {
  min2 = arrayItems[i]
  }
  }

Dynamic-Programming/tests/MaxProductOfThree.test.js

@@ -15,3 +15,56 @@ describe('MaxProductOfThree', () => {
  expect(maxProductOfThree([10, -6, 5, 3, 1, -10])).toBe(600)
  })
 })
+
+// Tests using random arrays of size 3 to 5, with values rangin from -4 to 4
+// The output is compared to a slower function that calculates all possible products of 3 numbers in the array and returns the largest one
+describe('MaxProductOfThree, random arrays of size 3 to 5', () => {
+ // Slower function that operates in O(n^3), where n is the length of the input array.
+ // Calculates all possible products of 3 numbers in the array and returns the largest
+ function completeMaxThree (array) {
+ let maximumProduct = null
+ for (let i = 0; i < array.length - 2; i++) {
+ for (let j = i + 1; j < array.length - 1; j++) {
+ for (let k = j + 1; k < array.length; k++) {
+ const currentProduct = array[i] * array[j] * array[k]
+ if (maximumProduct === null || currentProduct > maximumProduct) {
+ maximumProduct = currentProduct
+ }
+ }
+ }
+ }
+ return maximumProduct
+ }
+
+ // Set up consts for the tests
+ const maxValue = 4
+ const minValue = -4
+ const maxLength = 5
+ const minLength = 3
+ const numberOfRandomTests = 5000
+
+ // Run each test
+ for (let i = 0; i < numberOfRandomTests; i++) {
+ const arr = []
+ // Randomize the length of the array in the current test
+ const length = Math.floor(Math.random() * (maxLength - minLength) + minLength)
+
+ // Fill the array with random values in the specified range
+ for (let j = 0; j < length + 1; j++) {
+ arr.push(Math.floor(Math.random() * (maxValue - minValue) + minValue))
+ }
+
+ // Calculate the actual max product, slow but completely
+ const expectedProduct = completeMaxThree(arr)
+
+ // Set up the expectation
+ it('Expect the array ' + arr.toString() + ' to return the maximum three product of ' + expectedProduct, () => {
+ // Calculate the max three product using the function being tested
+ const actualProduct = maxProductOfThree(arr)
+
+ // Was unable to use expect().toBe(), since it sometimes compared 0 to -0, and that would not pass
+ // At the same time, standardjs forbid me from checking for === -0 to convert to 0
+ expect(actualProduct === expectedProduct).toBeTruthy()
+ })
+ }
+})