• Author: Graham Mitchell
• Filename: ReverseFactorial.java

Reverse Factorial

The factorial operator means to multiply all the values counting down from a given number. For example, 5! is equal to 120:

5! -> 5 * 4 * 3 * 2 * 1 -> 120

Write a static method called factBack() that can undo a factorial. That is, it will return the original number that was "factorialed", or -1 if the number isn't a perfect factorial. You can do this by dividing by increasingly-larger numbers until only 1 is left:

120: 120/2 -> 60/3 -> 20/4 -> 5/5 -> 1

150: 150/2 -> 75/3 -> 25/4? -> -1

Preconditions:

• The number will be greater than 0.

Examples:

• factBack(120) returns 5
• factBack(150) returns -1
• factBack(3628800) returns 10
• factBack(6) returns 3

Files Needed

• ReverseFactorial.java

©2003–2016 Graham Mitchell

This assignment is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.