Statistics

Problem Statement for "TheLuckyNumbers"

Problem Statement

John thinks 4 and 7 are lucky digits, and all other digits are not lucky. A lucky number is a number that contains only lucky digits in decimal notation.

You are given ints a and b. Return the number of lucky numbers between a and b, inclusive.

Definition

Class:
TheLuckyNumbers
Method:
count
Parameters:
int, int
Returns:
int
Method signature:
int count(int a, int b)
(be sure your method is public)

Constraints

  • a will be between 1 and 1,000,000,000, inclusive.
  • b will be between a and 1,000,000,000, inclusive.

Examples

  1. 1

    10

    Returns: 2

    There are only two lucky numbers among the first ten positive integers.

  2. 11

    20

    Returns: 0

    But there are none among the next ten.

  3. 74

    77

    Returns: 2

    These two numbers are lucky. There are no additional lucky numbers between them.

  4. 1000000

    5000000

    Returns: 64

  5. 1

    1000000000

    Returns: 1022

  6. 42

    68

    Returns: 2

  7. 1

    35

    Returns: 2

  8. 25

    70

    Returns: 2

  9. 59

    79

    Returns: 2

  10. 63

    65

    Returns: 0

  11. 42

    18468

    Returns: 28

  12. 335

    26501

    Returns: 24

  13. 170

    15725

    Returns: 24

  14. 479

    29359

    Returns: 20

  15. 963

    24465

    Returns: 16

  16. 42

    18468

    Returns: 28

  17. 6335

    26501

    Returns: 8

  18. 15725

    19170

    Returns: 0

  19. 11479

    29359

    Returns: 0

  20. 24465

    26963

    Returns: 0

  21. 42

    900018467

    Returns: 1020

  22. 6335

    900026500

    Returns: 1000

  23. 19170

    900015724

    Returns: 992

  24. 11479

    900029358

    Returns: 992

  25. 26963

    900024464

    Returns: 992

  26. 47474

    774774747

    Returns: 908

  27. 4

    777777777

    Returns: 1022

  28. 7

    774747747

    Returns: 939

  29. 5

    777474760

    Returns: 979

  30. 77447904

    774479991

    Returns: 464

  31. 447747444

    447747444

    Returns: 1

  32. 447747443

    447747445

    Returns: 1

  33. 447747443

    447747443

    Returns: 0

  34. 4

    999999997

    Returns: 1022

  35. 1

    999999999

    Returns: 1022

  36. 10

    1000000000

    Returns: 1020

  37. 1

    999921921

    Returns: 1022

  38. 1

    100000000

    Returns: 510

  39. 1

    777777777

    Returns: 1022

  40. 100000000

    1000000000

    Returns: 512

  41. 500000

    500000000

    Returns: 672

  42. 10000000

    1000000000

    Returns: 768

  43. 50000

    500000000

    Returns: 720

  44. 500

    850

    Returns: 4

  45. 525

    12500

    Returns: 20

  46. 4

    7

    Returns: 2

  47. 1

    74703586

    Returns: 414

  48. 7

    1000000000

    Returns: 1021

  49. 4

    4

    Returns: 1

  50. 7

    999999999

    Returns: 1021

  51. 7

    7

    Returns: 1

  52. 50

    51

    Returns: 0

  53. 17

    1000000000

    Returns: 1020

  54. 4

    1000000000

    Returns: 1022

  55. 77

    1000000000

    Returns: 1017

  56. 1

    4447

    Returns: 16

  57. 2778

    714642470

    Returns: 752

  58. 7

    777777777

    Returns: 1021

  59. 62419

    987654321

    Returns: 976

  60. 999999999

    1000000000

    Returns: 0

  61. 1

    605

    Returns: 10

  62. 781282001

    972285889

    Returns: 0

  63. 77

    777777777

    Returns: 1017

  64. 8

    10

    Returns: 0

  65. 1

    2

    Returns: 0

  66. 1

    44234523

    Returns: 254

  67. 1

    47

    Returns: 4

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