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){
 constn=arrayItems.length
 if(n<3)thrownewError('Triplet cannot exist with the given array')
 letmax1=arrayItems[0]
-letmax2=-1
-letmax3=-1
+letmax2=null
+letmax3=null
 letmin1=arrayItems[0]
-letmin2=-1
+letmin2=null
 for(leti=1;i<n;i++){
 if(arrayItems[i]>max1){
 max3=max2
 max2=max1
 max1=arrayItems[i]
-}elseif(max2===-1||arrayItems[i]>max2){
+}elseif(max2===null||arrayItems[i]>max2){
 max3=max2
 max2=arrayItems[i]
-}elseif(max3===-1||arrayItems[i]>max3){
+}elseif(max3===null||arrayItems[i]>max3){
 max3=arrayItems[i]
 }
 if(arrayItems[i]<min1){
 min2=min1
 min1=arrayItems[i]
-}elseif(min2===-1||arrayItems[i]<min2){
+}elseif(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
+functioncompleteMaxThree(array){
+letmaximumProduct=null
+for(leti=0;i<array.length-2;i++){
+for(letj=i+1;j<array.length-1;j++){
+for(letk=j+1;k<array.length;k++){
+constcurrentProduct=array[i]*array[j]*array[k]
+if(maximumProduct===null||currentProduct>maximumProduct){
+maximumProduct=currentProduct
+}
+}
+}
+}
+returnmaximumProduct
+}
+
+// Set up consts for the tests
+constmaxValue=4
+constminValue=-4
+constmaxLength=5
+constminLength=3
+constnumberOfRandomTests=5000
+
+// Run each test
+for(leti=0;i<numberOfRandomTests;i++){
+constarr=[]
+// Randomize the length of the array in the current test
+constlength=Math.floor(Math.random()*(maxLength-minLength)+minLength)
+
+// Fill the array with random values in the specified range
+for(letj=0;j<length+1;j++){
+arr.push(Math.floor(Math.random()*(maxValue-minValue)+minValue))
+}
+
+// Calculate the actual max product, slow but completely
+constexpectedProduct=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
+constactualProduct=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()
+})
+}
+})