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  1. package main
  2. import (
  3. 	"fmt"
  4. )
  5.  
  6. type PrimeGenerator struct {
  7. 	Next func() uint32
  8. }
  9.  
  10. func NewPrimeGenerator() *PrimeGenerator {
  11. 	primeGenerator := PrimeGenerator{}
  12.  
  13. 	multiples := map[uint32]uint32{}
  14. 	var num uint32
  15. 	primeGenerator.Next = func() uint32 {
  16. 		if num == 0 {
  17. 			num = 1
  18. 			return 2
  19. 		}
  20.  
  21. 		for ;; {
  22. 		    num += 2
  23.  
  24. 			factor, hasFactor := multiples[num]
  25. 			if hasFactor {
  26. 				delete(multiples, num)
  27. 			} else {
  28. 				factor = num << 1
  29. 			}
  30.  
  31. 			for newNum := num + factor; ; newNum += factor {
  32. 				_, hasNewFactor := multiples[newNum]
  33. 				if !hasNewFactor {
  34. 					multiples[newNum] = factor
  35. 					break
  36. 				}
  37. 			}
  38.  
  39. 			if !hasFactor {
  40. 				return num
  41. 			}
  42. 		}
  43. 	}
  44.  
  45. 	return &primeGenerator
  46. }
  47.  
  48. func main() {
  49. 	n := 1000000
  50. 	primeGenerator := NewPrimeGenerator()
  51. 	for i := 1; i < n; i++ {
  52. 		primeGenerator.Next()
  53. 	}
  54. 	fmt.Printf("%d番目の素数: %d", n, primeGenerator.Next())
  55. }
Success #stdin #stdout 2.1s 49712KB
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1000000番目の素数: 15485863
https://ideone.com/zjVCgk
language:
Go (go 1.12.1)
created:
7 years ago
visibility:
public

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