Finding all prime numbers within a range












0












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I am trying to find all primes less than 2,000,000 and sum them together. My code currently takes 1'36" to run. Is there a faster way to get my solution?



The logic I am following in this code is make a list of all primes I have found. Then check that every odd number less than 2,000,000 is not divisible by any of the primes in my list. If that is the case I am calling the number prime.



package main                                          

import ("fmt"
"time"
)

func find_primes(max int) int {
// list of all primes that we find
var primes int
primes = append(primes, 2)

var is_prime = true
for i:=3; i<=max; i++ {
is_prime = false
// only odds can be prime
if i%2 != 0 {
is_prime = true
// should not be divisible by any previous
// prime numbers
for _, x := range primes {
if i%x == 0 {
is_prime = false
break
}
}
}
if is_prime {
primes = append(primes, i)
}
}
return primes
}

// just sume up all of the primes
func sum_primes(primes int) int {
var total int = 0
for _, x := range primes {
total = total + x
}
return total
}

func main() {
start := time.Now()
// find all primes less than 2,000,000
primes := find_primes(2000000)
sum := sum_primes(primes)
fmt.Println(sum)
t := time.Now()
elapsed := t.Sub(start)
fmt.Println(elapsed)
}








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    $begingroup$


    I am trying to find all primes less than 2,000,000 and sum them together. My code currently takes 1'36" to run. Is there a faster way to get my solution?



    The logic I am following in this code is make a list of all primes I have found. Then check that every odd number less than 2,000,000 is not divisible by any of the primes in my list. If that is the case I am calling the number prime.



    package main                                          

    import ("fmt"
    "time"
    )

    func find_primes(max int) int {
    // list of all primes that we find
    var primes int
    primes = append(primes, 2)

    var is_prime = true
    for i:=3; i<=max; i++ {
    is_prime = false
    // only odds can be prime
    if i%2 != 0 {
    is_prime = true
    // should not be divisible by any previous
    // prime numbers
    for _, x := range primes {
    if i%x == 0 {
    is_prime = false
    break
    }
    }
    }
    if is_prime {
    primes = append(primes, i)
    }
    }
    return primes
    }

    // just sume up all of the primes
    func sum_primes(primes int) int {
    var total int = 0
    for _, x := range primes {
    total = total + x
    }
    return total
    }

    func main() {
    start := time.Now()
    // find all primes less than 2,000,000
    primes := find_primes(2000000)
    sum := sum_primes(primes)
    fmt.Println(sum)
    t := time.Now()
    elapsed := t.Sub(start)
    fmt.Println(elapsed)
    }








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      $begingroup$


      I am trying to find all primes less than 2,000,000 and sum them together. My code currently takes 1'36" to run. Is there a faster way to get my solution?



      The logic I am following in this code is make a list of all primes I have found. Then check that every odd number less than 2,000,000 is not divisible by any of the primes in my list. If that is the case I am calling the number prime.



      package main                                          

      import ("fmt"
      "time"
      )

      func find_primes(max int) int {
      // list of all primes that we find
      var primes int
      primes = append(primes, 2)

      var is_prime = true
      for i:=3; i<=max; i++ {
      is_prime = false
      // only odds can be prime
      if i%2 != 0 {
      is_prime = true
      // should not be divisible by any previous
      // prime numbers
      for _, x := range primes {
      if i%x == 0 {
      is_prime = false
      break
      }
      }
      }
      if is_prime {
      primes = append(primes, i)
      }
      }
      return primes
      }

      // just sume up all of the primes
      func sum_primes(primes int) int {
      var total int = 0
      for _, x := range primes {
      total = total + x
      }
      return total
      }

      func main() {
      start := time.Now()
      // find all primes less than 2,000,000
      primes := find_primes(2000000)
      sum := sum_primes(primes)
      fmt.Println(sum)
      t := time.Now()
      elapsed := t.Sub(start)
      fmt.Println(elapsed)
      }








      share









      $endgroup$




      I am trying to find all primes less than 2,000,000 and sum them together. My code currently takes 1'36" to run. Is there a faster way to get my solution?



      The logic I am following in this code is make a list of all primes I have found. Then check that every odd number less than 2,000,000 is not divisible by any of the primes in my list. If that is the case I am calling the number prime.



      package main                                          

      import ("fmt"
      "time"
      )

      func find_primes(max int) int {
      // list of all primes that we find
      var primes int
      primes = append(primes, 2)

      var is_prime = true
      for i:=3; i<=max; i++ {
      is_prime = false
      // only odds can be prime
      if i%2 != 0 {
      is_prime = true
      // should not be divisible by any previous
      // prime numbers
      for _, x := range primes {
      if i%x == 0 {
      is_prime = false
      break
      }
      }
      }
      if is_prime {
      primes = append(primes, i)
      }
      }
      return primes
      }

      // just sume up all of the primes
      func sum_primes(primes int) int {
      var total int = 0
      for _, x := range primes {
      total = total + x
      }
      return total
      }

      func main() {
      start := time.Now()
      // find all primes less than 2,000,000
      primes := find_primes(2000000)
      sum := sum_primes(primes)
      fmt.Println(sum)
      t := time.Now()
      elapsed := t.Sub(start)
      fmt.Println(elapsed)
      }






      go





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