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Commit 6aa3314

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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
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‎Dynamic-Programming/MaxProductOfThree.js‎

Lines changed: 6 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -10,25 +10,25 @@ export function maxProductOfThree (arrayItems) {
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const n = arrayItems.length
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if (n < 3) throw new Error('Triplet cannot exist with the given array')
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let max1 = arrayItems[0]
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let max2 = -1
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let max3 = -1
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let max2 = null
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let max3 = null
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let min1 = arrayItems[0]
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let min2 = -1
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let min2 = null
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for (let i = 1; i < n; i++) {
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if (arrayItems[i] > max1) {
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max3 = max2
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max2 = max1
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max1 = arrayItems[i]
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} else if (max2 === -1 || arrayItems[i] > max2) {
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} else if (max2 === null || arrayItems[i] > max2) {
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max3 = max2
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max2 = arrayItems[i]
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} else if (max3 === -1 || arrayItems[i] > max3) {
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} else if (max3 === null || arrayItems[i] > max3) {
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max3 = arrayItems[i]
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}
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if (arrayItems[i] < min1) {
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min2 = min1
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min1 = arrayItems[i]
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} else if (min2 === -1 || arrayItems[i] < min2) {
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} else if (min2 === null || arrayItems[i] < min2) {
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min2 = arrayItems[i]
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}
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}

‎Dynamic-Programming/tests/MaxProductOfThree.test.js‎

Lines changed: 53 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -15,3 +15,56 @@ describe('MaxProductOfThree', () => {
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expect(maxProductOfThree([10, -6, 5, 3, 1, -10])).toBe(600)
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})
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})
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// Tests using random arrays of size 3 to 5, with values rangin from -4 to 4
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// The output is compared to a slower function that calculates all possible products of 3 numbers in the array and returns the largest one
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describe('MaxProductOfThree, random arrays of size 3 to 5', () => {
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// Slower function that operates in O(n^3), where n is the length of the input array.
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// Calculates all possible products of 3 numbers in the array and returns the largest
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function completeMaxThree (array) {
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let maximumProduct = null
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for (let i = 0; i < array.length - 2; i++) {
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for (let j = i + 1; j < array.length - 1; j++) {
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for (let k = j + 1; k < array.length; k++) {
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const currentProduct = array[i] * array[j] * array[k]
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if (maximumProduct === null || currentProduct > maximumProduct) {
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maximumProduct = currentProduct
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}
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}
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}
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}
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return maximumProduct
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}
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// Set up consts for the tests
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const maxValue = 4
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const minValue = -4
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const maxLength = 5
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const minLength = 3
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const numberOfRandomTests = 5000
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// Run each test
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for (let i = 0; i < numberOfRandomTests; i++) {
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const arr = []
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// Randomize the length of the array in the current test
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const length = Math.floor(Math.random() * (maxLength - minLength) + minLength)
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// Fill the array with random values in the specified range
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for (let j = 0; j < length + 1; j++) {
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arr.push(Math.floor(Math.random() * (maxValue - minValue) + minValue))
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}
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// Calculate the actual max product, slow but completely
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const expectedProduct = completeMaxThree(arr)
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// Set up the expectation
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it('Expect the array ' + arr.toString() + ' to return the maximum three product of ' + expectedProduct, () => {
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// Calculate the max three product using the function being tested
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const actualProduct = maxProductOfThree(arr)
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// Was unable to use expect().toBe(), since it sometimes compared 0 to -0, and that would not pass
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// At the same time, standardjs forbid me from checking for === -0 to convert to 0
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expect(actualProduct === expectedProduct).toBeTruthy()
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})
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}
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})

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