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
0)
1
10
Returns: 2
There are only two lucky numbers among the first ten positive integers.
1)
11
20
Returns: 0
But there are none among the next ten.
2)
74
77
Returns: 2
These two numbers are lucky. There are no additional lucky numbers between them.
3)
1000000
5000000
Returns: 64
coding hangover 