TheLuckyNumbersLevelOne | Topcoder Archive

Problem Statement

The digits 4 and 7 are lucky digits, and all other digits are unlucky. A first level lucky number is a positive integer whose decimal representation is a palindrome that contains only lucky digits. A palindrome is a number that reads the same forward and backward. John and Brus would like to count the number of first level lucky numbers within a specified range.

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

Definition

Class:: TheLuckyNumbersLevelOne
Method:: find
Parameters:: long, long
Returns:: long
Method signature:: long find(long a, long b)
(be sure your method is public)

Constraints

a will be between 1 and 10^18, inclusive.
b will be between a and 10^18, inclusive.

Examples

```
1
```
```
100
```
```
Returns: 4
```
The first level lucky numbers within this range are 4, 7, 44 and 77.
```
45
```
```
54
```
```
Returns: 0
```
There are no first level lucky numbers here.
```
477444774
```
```
477444774
```
```
Returns: 1
```
The given range contains only one integer and it is a first level lucky number.
```
456789123
```
```
789123456
```
```
Returns: 24
```

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