freeCodeCamp Challenge Guide: Sum All Primes

Guide
#36

Based my work on a paragraph here…
This is the first time I’ve felt compelled to post my solution. Since I’m following tutorials they are usually not significantly different to be covering any new territory, but I got out in the weeds on this one and some how still made it back, 233 lines later…

//helper functions
function isItEven(n) {
  //  Try 2: is an even number and it will be divisible by 2, therefore it is not prime.
  if (n === 1) {
    return;
  }
  if (n === 2) {
    return n;
  }
  if (n % 2 !== 0) {
    console.log(n);
    return n;
  }
} //end of isItEven

function isItTHREED(n) {
  //  [based my work off a paragraph here..](https://www.thoughtco.com/how-to-determine-number-is-prime-2312518)
  if (n === 3) {
    return n;
  }
  //  Try 3.  Take the number, and add the digits up, when those digits are divisible by 3, the number is not prime.
  //          Take 2469, those digits add up to 21, and 21 is divisible by 3, therefore 2469 is not a prime number.
  console.log("3s", n);
  n = n.toString();
  var digitONE = Number(n.charAt(0));
  var digitTWO = Number(n.charAt(1));
  var digitTHREE = Number(n.charAt(2));
  var digitFOUR = Number(n.charAt(3));
  console.log("digits", digitONE);
  console.log("digits", digitTWO);
  console.log("digits", digitTHREE);
  console.log("digits", digitFOUR);
  var testing = digitONE + digitTWO + digitTHREE + digitFOUR;
  console.log(testing);
  n = Number(n);
  if (testing % 3 !== 0) {
    return n;
  }
} //end of isItTHREED

function isItFOURED(n) {
  //  https://www.thoughtco.com/how-to-determine-number-is-prime-2312518
  var fourTrap = [];
  n = n.toString();
  var digitLAST = Number(n.charAt(n.length));
  var digitNEXTtoLast = Number(n.charAt(n.length - 1));
  console.log("digits", digitLAST);
  console.log("digits", digitNEXTtoLast);
  var testing = digitLAST + digitNEXTtoLast;
  console.log(testing);
  n = Number(n);
  if (testing % 4 === 0) {
    fourTrap.push(n);
    console.log("fourThrap", fourTrap);
  }
  if (testing % 4 !== 0) {
    return n;
  }
} //end of isItFOURED

function isItFIVED(n) {
  if (n === 5) {
    return n;
  }
  var fifthTrap = [];
  var fifthLast = n.toString();
  console.log(n);
  var digitLAST = Number(fifthLast.charAt(fifthLast.length - 1));
  var testing = digitLAST;
  console.log("testLOG", testing);
  n = Number(n);
  if (testing === 5 || testing === 0) {
    fifthTrap.push(n);
    console.log("traptFIVE", fifthTrap);
  }
  if (testing !== 5 && testing !== 0) {
    return n;
  }
} //end of isItFIVED

function isItSeveneD(n) {
  //  Try 2: is an even number and it will be divisible by 2, therefore it is not prime.
  if (n === 7) {
    return n;
  }
  if (n % 7 !== 0) {
    console.log(n);
    return n;
  }
} //end of isItSeveneD

function isItElevened(n) {
  //  Try 2: is an even number and it will be divisible by 2, therefore it is not prime.
  if (n === 11) {
    return n;
  }
  if (n % 11 !== 0) {
    console.log(n);
    return n;
  }
} //end of isItElevened

function isIt13th(n) {
  //  Try 2: is an even number and it will be divisible by 2, therefore it is not prime.
  if (n === 13) {
    return n;
  }
  if (n % 13 !== 0) {
    console.log(n);
    return n;
  }
} //end of isIt13th

function isIt17th(n) {
  //  Try 2: is an even number and it will be divisible by 2, therefore it is not prime.
  if (n === 17) {
    return n;
  }
  if (n % 17 !== 0) {
    console.log(n);
    return n;
  }
} //end of isIt17th

function isIt19th(n) {
  //  Try 2: is an even number and it will be divisible by 2, therefore it is not prime.
  if (n === 19) {
    return n;
  }
  if (n % 19 !== 0) {
    console.log(n);
    return n;
  }
} //end of isIt19th

function isIt23rd(n) {
  //  Try 2: is an even number and it will be divisible by 2, therefore it is not prime.
  if (n === 23) {
    return n;
  }
  if (n % 23 !== 0) {
    console.log(n);
    return n;
  }
} //end of isIt23rd

function isIt29(n) {
  //  Try 2: is an even number and it will be divisible by 2, therefore it is not prime.
  if (n === 29) {
    return n;
  }
  if (n % 29 !== 0) {
    console.log(n);
    return n;
  }
} //end of isIt29

function isItThirtyONED(n) {
  if (n === 31) {
    return n;
  }
  if (n % 31 !== 0) {
    console.log(n);
    return n;
  }
} //end of isItThirtyONED

function sumPrimes(num) {
  var primes = [];
  var i = 1;
  while (i < num + 1) {
    primes.push(i);
    i++;
  }
  console.log("primes", primes);
  primes = primes.filter(isItEven);

  //  Try 3.  Take the number, and add the digits up, when those digits are divisible by 3, the number is not prime.
  //          Take 2469, those digits add up to 21, and 21 is divisible by 3, therefore 2469 is not a prime number.
  primes = primes.filter(isItTHREED);
  console.log("isItTHREED", primes);

  //  Try fours.
  primes = primes.filter(isItFOURED);
  console.log("isItFOURED", primes);

  //  Try fives
  primes = primes.filter(isItFIVED);
  console.log(primes);

  //  Try 7
  primes = primes.filter(isItSeveneD);
  console.log(primes);

  //  Try 11
  primes = primes.filter(isItElevened);
  console.log(primes);

  //  Try 13
  primes = primes.filter(isIt13th);
  console.log(primes);

  //  Try 13
  primes = primes.filter(isIt17th);
  console.log(primes);
  
  //  Try 19
  primes = primes.filter(isIt19th);
  console.log(primes);

  //  Try 23
  primes = primes.filter(isIt23rd);
  console.log(primes);

    //  Try 29
  primes = primes.filter(isIt29);
  console.log(primes);
  
  //  Try 31
  primes = primes.filter(isItThirtyONED);
  console.log(primes);

  //might extract the anounoum function.. may also use it to filter out evens?
  var reducted = primes.reduce((total, amount) => total + amount);
  num = Number(reducted);
  //console.log(num);
  return num;
} //sumPrimes

sumPrimes(10); // should return 17.
//sumPrimes(100); // should return 17.
//sumPrimes(977); // should return 73156.
//2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41
#37 

function sumPrimes(num) {
  //declare vars. One to store an array of prime numbers and another to store the sum of these numbers. 
 var primes = [];
 var primeSum = 0;
  //create a function to check for prime numbers
  function isPrime(num) {
    if(num < 2) 
      return false;
    for (var i = 2; i < num; i++) {
      if(num%i===0)
        return false;
    }
    return true;
  }
  //increment through all numbers less than num and pass i to the function isPrime. If true, then push the number to the var primes.
  for(var i = 0; i <= num; i++){
    if(isPrime(i)) {
      primes.push(i);
    }
  }
 //Once the array of prime numbers has been created, iterate through this array and add all the numbers together and store in the var primeSum. 
 for (var j = 0; j < primes.length; j++){
    primeSum += primes[j];
 }
  //return the var prime Sum. 
  return primeSum;
}

sumPrimes(977);
#38

A little tricky, but in the end I found this solution:

Captura.PNG795×473 13.4 KB

#39

I believe this solution is more optimal than the advanced solution:

function sumPrimes(num) {
  var sum = 0;
  for(var i = 0; i <= num;i++){
    if(IsPrime(i)){
      sum += i;
    }
  }
  return sum;
}

function IsPrime(n){
  if(n <= 1) return false;
  for(var j = 2; Math.pow(j,2) <= n;j++){
    if(n % j === 0) {
      return false;
    }
  }
  return true;
}

Time complexity: O(n * sqrt(n))
Space Complexity: O(1)

1 Like
#40

I agree. I had a similar solution:

function sumPrimes(num) {
  var sum = 0;
  
  function isPrime(x) {
    var factors = [];
    for (var i = 1; i <= x; i++) {
      if (x % i == 0) {
        factors.push(i);
      }
    }
    if (factors.length == 2) {
      return true;
    } else {
      return false;
    }
  }
  
  for (var j = 1; j <= num; j++) {
    if (isPrime(j)) {
      sum += j;
    } 
  }
  
  return sum;
}

sumPrimes(10);
#41

A simple one:

function sumPrimes(num) {
  if(num < 2) return 0;
  //taking 2 since it is only even prime number --> will save one cycle of loop
  var sum = 2;
  var flag = false;
  for(var i = 3; i <= num;) {
    flag = checkForPrime(i);
    if (flag === false) {
      sum += i;
    }
    // to check only odd numbers
    i += 2;
  }
  return sum;
}

function checkForPrime(num) {
  // a nuber has all the factors within it's sqare root
  var sqrt = Math.sqrt(num);
  var flag = false;
  for(var i = 3; i <= sqrt;) {
    if(num % i === 0) flag = true;
    i = i + 2;
  }
  return flag;
}
#42

Here is my solution, but I can’t fix why 2 didn’t appears as prime number.
I use this algorithm to check if the number is prime or not:

function sumPrimes(num) {
var arr = [];
var sum = 2; // I can't fix why 2 didn't appears as prime number in my solution
for (var i=0;i<=num;i++) {
arr.push(i);
}
for (i=0;i<arr.length;i++) {
var sqrAnValue = Math.ceil(Math.sqrt(arr[i]));
for(var j=2;j<=sqrAnValue;j++) {
if(arr[i]%j === 0) {
break;
} else if (arr[i]%j !== 0 && j == sqrAnValue)  {
sum += arr[i];
}
}
}
return sum;
#43

:beginner: Basic Code Solution:

function sumPrimes(num) {
    var sum = 0;
    var divider;

    for (var i = 2; i <= num; i++) {
      divider = 2;
        while (i % divider !== 0) {		
            divider++;
        }
        if (i === divider) {
            sum += i;
        }
    }

    return sum;
}
2 Likes
#44

Basic solution, but it works! :grinning:

function sumPrimes(num) {
  var cont = 0;
  var res = 0;
  for(var i = 2; i <= num; i++){
    for(var j = 1; j <= i; j++){
      if(i%j === 0){
        cont++;
      } 
    }  
    if(cont === 2){
      res += i;
    }
    cont = 0;
  }
  return res;
}

sumPrimes(5);
1 Like
#45 
function sumPrimes(num) {
  
  var arr = [];  
  
  function isPrime(num) {
      if(num < 2) return false;
      for (var i = 2; i < num; i++) {
          if(num%i==0)
              return false;
      }
      return true;
  }

  for(var i=0;i<=num;i++){
    if (isPrime(i)){
      arr.push(i);
    }
  }
  
  return arr.reduce(function(sum, value) {
    return sum + value;
  }, 0);
  
}

sumPrimes(977);
#46

To determine if a number n is prime, you only need to try dividing n by primes, since all the composites (non-primes) are multiples of primes you already tested.

Also, once the prime p you are testing exceeds the square root of n, and n % p has always had a remainder, you don’t need to go any further — p (or higher) would have to be multiplied by a lower value to possibly equal n, and you’ve already tested all the possible lower values! At this point, you know that n is prime.

function sumPrimes(num) {
  var sum = 2;
  var p = [2];
  
  for (var n = 3; n <= num; n++) {
    for (var i = 0; i < p.length; i++) {
      if (n % p[i] === 0) break;
      if (n / p[i] < p[i]) {
        sum += n;
        p.push(n);
        break;
      }
    }
  }
  return sum;
}
2 Likes
#47 
function sumPrimes(num) {
  var sumPrimez = 0;
  var count = 0;
  var arr = [0];
  for(var i=1;i<=num;i++){
    for (var j=1;j<=i;j++){
      if((i%j)==0){
        count+=1;
      }      
    }
  arr.push(count);
  count = 0;
}
for(var i=0;i<arr.length;i++)
{
    if (arr[i]==2){
        sumPrimez+=i;
    }
}
return sumPrimez;
}

sumPrimes(977);

Simple but not so efficient. How do you guys come up with these way cooler algorithms ? :tired_face:

#48

function sumPrimes(num) {
var i=1,sum=0;
while(num>=i){
if(isPrime(i))sum+=i;
i++;
}

return sum;
}
function isPrime(num) {
for(var i = 2; i < num; i++)
if(num % i === 0) return false;
return num !== 1;
}
sumPrimes(10);

here’s my code

#49 
function sumPrimes(num) {
  var prim=[],primtst;
 for(var i=2 ;i<=num;i++){
  primtst=0;
   for(var j=1;j<=i;j++){
   if(i%j==0){
    primtst++;
   }
   }
  if(primtst==2){
    prim.push(i);
  }
 

}
return prim.reduce(function(a,b){return a+=b;});
}

sumPrimes(10);
#50

Hello everyone,

'Cause I didn’t saw something exactly like this, I think I’ll add my solution in the pool:

    function sumPrimes(num) {
      
      var temp = [],
          primes = [],
          sumUp;
      
      function zPrime(num) {
        for (var x = 2; x < num; x++) {
          if(num < 2) return false;
          if(num % x === 0) return false;
        } return true;
      }  
      for (var y = 2, z = 0; y <= num, z < num-1; y++, z++){
        if(y <= num) temp.push(y);
        if(zPrime(temp[z]) === true) primes.push(temp[z]);
      }
      sumUp = primes.reduce(function(a,b){
        return a + b;
      });
      return sumUp;
    }
    //There is no spoon!
    sumPrimes(1000);
#51

stackoverflow pointed me to two different methods

function sumPrimes(num) {
  var PrimeArr=[2];
  if (num <= 1){
    return false;
  }else if (num === 2){
    PrimeArr.push(2);
  } else { 
    for (var i=3;i<=num;i++){
    for (var j=2;j<i;j++){
      if (i%j===0){break;}
      if (j===i-1){
      PrimeArr.push(i);}
    }
    }
      }
 
  return PrimeArr.reduce(function (sum,value){
    return sum +=value;
  });
}

second one is sqrt method

function sumPrimes(num) {
  var PrimeArr=[2,3];
  if (num <= 1){
    return false;
  }else if (num === 2){
    PrimeArr.push(2);
  } else {
    for (var i=2;i<=num;i++){
    var sq=Math.floor(Math.sqrt(i));
    for (var j = 2; j <= sq; j++){
        if (i % j === 0){break;}
        if (j===sq){
        PrimeArr.push(i);}
    }
    }
      }

  return PrimeArr.reduce(function (sum,value){
    return sum +=value;
  });
}
#52 
function sumPrimes(num) {
  
  //[STEP 1]An array to store all numbers from 0 - 'num'
  var arr=[];
  
  //[STEP 2]A variable to store the sum of all primes numbers
  var total = 0;

  /*[STEP 3] Loops 'num' number of times and 'pushes' all
    numbers from 0 to 'num' into the array 'arr' */
  for(var j = 1; j <= num; j++){
   arr.push(j); 
  }
  
 //[STEP 4.1] loop through the array 'arr' to test each number for prime
 for(var i = 0; i < arr.length; i++) {
   /*[STEP 4.2] pass each number from the 
     array 'arr' into the 'isPrime' function (defined below)
     to check if it is a prime number.
     (Go to isPrime function below for next step) */
   if(isPrime(arr[i]) == true){
 
     //[STEP 6] If 'true' the number is added to total
     total+= arr[i];
   }
  }
  
  /*[Step 7] After loop is complete, return 'total' 
    which stores the sum of all the primes number until 'num' */
  return total;
    }

//[STEP 5] returns true or false if the number is prime or not.
function isPrime(value) {
    for(var i = 2; i < value; i++) {
        if(value % i === 0) {
            return false;
        }
    }
    return value > 1;
}

sumPrimes(10);
#53

What about this solution?

function isPrime(num) {
  for (let i = 2; i < num; i++) {
    if (num % i === 0) {
      return false;
    }
  }
  return true;
}

function sumPrimes(num) {
  var sum = 0;
  for (let i = 2; i <= num; i++) {
    if (isPrime(i)) {
      sum += i;
    }
  }
  return sum;
}
7 Likes
#55
#56 
function sumPrimes(num) {
  let primeArr = [];
  nextPrime:
  for (let i = 2; i <= num; i++) {
    for (let j = 2; j < i; j++) {
      if (i % j == 0) continue nextPrime;
    }
    primeArr.push(i);
  }
  return primeArr.reduce((acc, curr) => acc + curr);
}

sumPrimes(10);