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The sieve of eratosthenes

R

#!/usr/bin/env Rscript

# Sieve of Eratosthenes in R
# Written by Rob Hoelz

nextPrime <- function(primes, currPrime) {
  currPrime <- currPrime + 1
  while(primes[currPrime] == 0) {
    currPrime <- currPrime + 1
  }
  currPrime
}

printPrimes <- function(primes) {
  for (i in 1:length(primes)) {
    if(primes[i] == 1) cat(i, " ", sep="") else 0
  }
  cat("\n", sep="")
}

sieve <- function(limit) {
  currPrime <- 2
  primes <- c(0, rep(1, times=(limit-1)))
  while (currPrime * currPrime <= limit) {
    primes[seq(currPrime * 2, limit, by=currPrime)] = 0
    currPrime <- nextPrime(primes, currPrime)
  }
  printPrimes(primes)
}

args <- as.integer(commandArgs(TRUE))
if(length(args) > 0) {
    sieve(args[1])
}

back to Eratosthenes page

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