Having trouble with my approach to Project Euler #8, it seems to have stopped working

Question

Having trouble with my approach to Project Euler #8, it seems to have stopped working

After tackling a challenging problem online, I successfully discovered the largest product of any 5 consecutive numbers within a 1000-digit number:

        var bignumber = "731671765313306249192251196744265747423553491949349698352031277450632623957831801698480186947885184385861560789112949495459501737958331952853208805511125406987471585238630507156932909632952274430435576689664895044524452316173185640309871112172238311362229893423380308135336276614282806444486645238749303589072962904915604407723907138105158593079608667017242712188399879790879227492190169972088809377665727333010533678812202354218097512545405947522435258490771167055601360483958644670632441572215539753697817977846174064955149290862569321978468622482839722413756570560574902614079729686524145358866881164271714799244429282308634656748139191231628245861786645835912456652947654568284891288314260769004224219022671055626317761111093705442175069416589604080719840385096241334462981230987879927244283625438";
    var bigarray = bignumber.split("");
    var prod = [];
    var buy = 1;
    var z = 4;
    for (var i = 0; i < bigarray.length; i+=z) {
      mult = bigarray[i];
      for (var x = 1; x <= z; x++) {
        mult *= bigarray[i+x];
      }
      prod.push(mult);
    }
    prod.sort(function(a, b){return b-a});
    document.write(prod[0]);

Fascinated by my discovery, I posted about it here, realizing later that this intriguing problem originated from Project Euler. Curious to explore further, I visited the official page here. It puzzled me that when I attempted to adjust the consecutive digits to 13 instead of 5 by changing z to 12, the solution was incorrect. Why did this modification lead to an unexpected outcome?

javascript arrays sorting for-loop numbers

Answer 1

Answer №1

The error lies in this specific portion of code:

for (var i = 0; i < bigarray.length; i+=z) {

:

To rectify the issue, adjust the loop condition to i < bigarray.length - z. This modification is necessary because the inner loop progresses up to z indices, so the outer loop must ensure that there are at least z elements remaining from index i.
Furthermore, modify the loop increment to i+=1. The rationale behind this adjustment is illustrated by considering the task of identifying the largest product of two successive digits in the input "1221". Your current algorithm calculates 1*2 = 2 and 2*1 = 2, while the correct solution should be 2*2 = 4, which can only be achieved by examining each input digit as a potential starting point.

After implementing these changes, you have the opportunity to optimize your algorithm further. One approach involves leveraging the mult value from the previous iteration.

Answer 2

The error lies in this specific portion of code:

for (var i = 0; i < bigarray.length; i+=z) {

:

To rectify the issue, adjust the loop condition to i < bigarray.length - z. This modification is necessary because the inner loop progresses up to z indices, so the outer loop must ensure that there are at least z elements remaining from index i.
Furthermore, modify the loop increment to i+=1. The rationale behind this adjustment is illustrated by considering the task of identifying the largest product of two successive digits in the input "1221". Your current algorithm calculates 1*2 = 2 and 2*1 = 2, while the correct solution should be 2*2 = 4, which can only be achieved by examining each input digit as a potential starting point.

After implementing these changes, you have the opportunity to optimize your algorithm further. One approach involves leveraging the mult value from the previous iteration.

Answer 3

Answer №2

Below are the steps you can take:

function calculateMaxProduct(s,n){
  return Math.max(...s.split("")
                      .map((_,i,a) => a.slice(i,i+n))
                      .slice(0,s.length-n+1)
                      .map(subArray => subArray.reduce((prev,curr) => +prev * +curr)));
}

var bigNum = "7316717653133062491922511967442657474235534919493496983520312774506326239578318016984801869478851843858615607891129494954595017379583319528532088055111254069874715852386305071569329096329522744304355766896648950445244523161731856403098711121722383113622298934233803081353362766142828064444866452387493035890729629049156044077239071381051585930796086670172427121883998797908792274921901699720888093776657273330100533678812202354218097512545405947522435258490771167055601360483958644670632441572215539753697817977846174064955149290862569321978468622482839722413756570560574902614079729686524145351004748216637048440319989000889524345065854122758866688116427171479924442928230863465674813919123162824586178664583591245665294765456828489128831426076900422421902267105562632111110937054421750694165896040807198403850962455444362981230987879927244284909188845801561660979191338754992005240636899125607176060588611646710940507754100225698315520005593572972571636269561882670428252483600823257530420752963450";
console.log(calculateMaxProduct(bigNum,13));

Answer 4

Below are the steps you can take:

function calculateMaxProduct(s,n){
  return Math.max(...s.split("")
                      .map((_,i,a) => a.slice(i,i+n))
                      .slice(0,s.length-n+1)
                      .map(subArray => subArray.reduce((prev,curr) => +prev * +curr)));
}

var bigNum = "7316717653133062491922511967442657474235534919493496983520312774506326239578318016984801869478851843858615607891129494954595017379583319528532088055111254069874715852386305071569329096329522744304355766896648950445244523161731856403098711121722383113622298934233803081353362766142828064444866452387493035890729629049156044077239071381051585930796086670172427121883998797908792274921901699720888093776657273330100533678812202354218097512545405947522435258490771167055601360483958644670632441572215539753697817977846174064955149290862569321978468622482839722413756570560574902614079729686524145351004748216637048440319989000889524345065854122758866688116427171479924442928230863465674813919123162824586178664583591245665294765456828489128831426076900422421902267105562632111110937054421750694165896040807198403850962455444362981230987879927244284909188845801561660979191338754992005240636899125607176060588611646710940507754100225698315520005593572972571636269561882670428252483600823257530420752963450";
console.log(calculateMaxProduct(bigNum,13));

Having trouble with my approach to Project Euler #8, it seems to have stopped working

Answer №1

Answer №2

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