TheLargestLuckyNumber | Topcoder Archive

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 an int n. Return the largest lucky number that is less than or equal to n.

Definition

Class:: TheLargestLuckyNumber
Method:: find
Parameters:: int
Returns:: int
Method signature:: int find(int n)
(be sure your method is public)

Constraints

n will be between 4 and 1,000,000, inclusive.

Examples

```
100
```
```
Returns: 77
```
77 is the largest lucky number that is not greater than 100.
```
75
```
```
Returns: 74
```
74 is the lucky number that immediately precedes 77.
```
5
```
```
Returns: 4
```
The smallest lucky number is 4.
```
474747
```
```
Returns: 474747
```
n is a lucky number.

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