/
primes.go
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/
primes.go
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// Copyright (c) 2019 Matúš Mrekaj.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package arrays
// GeneratePrimes generates all prime numbers from 2
// all the way up but no including upperBound.
// Time complexity is O(n log(log(n))), space complexity O(n)
func GeneratePrimes(upperBound int) []uint {
if upperBound < 3 {
return nil
}
isPrime := make([]bool, upperBound)
for i := range isPrime {
isPrime[i] = true
}
var primes []uint
for i := 2; i < len(isPrime); i++ {
if isPrime[i] {
primes = append(primes, uint(i))
for j := i; j < len(isPrime); j += i {
isPrime[j] = false
}
}
}
return primes
}