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Write a recursive method <code>factorial(n)</code>
that returns n × (n-1) × (n-2) × … × 3 × 2 &times 1. For example, <code>factorial(4)</code> should return 24 since that is the value of 1 × 2 × 3 × 4.

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Choices
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Correct answer
Template / Reference solution

public static \[long]\ factorial(\[int n]\) {
// base case
if (\[n == 0]\)
return \[1]\;

// reduction step
// note that n! = n * (n-1) * ... * 2 * 1 = n * ((n-1) * ... * 2 * 1)
return \[n]\ * factorial(\[n-1]\);
}

public static void main(String[] args) {
StdOut.println(factorial(4)); // should be 24
StdOut.println(factorial(10)); // should be 3628800
StdOut.println(factorial(20)); // watch for overflow. what return type?
}
Template / Reference solution

Java test suite
See manual

testMain();
test("factorial", 1);
test("factorial", 6);
test("factorial", 11);

C++ test suite
json list of stdin/args tests
e.g. [{"stdin":"hi", "args":["4", "5"]}, {"stdin":"noargs"}]
to just run once with no input use [{}]

C++ test suite
See manual

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Property	Value
Description html markup shown to student	Write a recursive method <code>factorial(n)</code> that returns n × (n-1) × (n-2) × … × 3 × 2 &times 1. For example, <code>factorial(4)</code> should return 24 since that is the value of 1 × 2 × 3 × 4.
Epilogue html markup shown when solved	remove
Public permissions	remove
Remarks Comments, history, license, etc.	remove
Engine
Choices json list of string, bool pairs e.g. `[["good", true], ["bad", false]]`
Correct answer
Template / Reference solution	public static \[long]\ factorial(\[int n]\) { // base case if (\[n == 0]\) return \[1]\; // reduction step // note that n! = n * (n-1) * ... * 2 * 1 = n * ((n-1) * ... * 2 * 1) return \[n]\ * factorial(\[n-1]\); } public static void main(String[] args) { StdOut.println(factorial(4)); // should be 24 StdOut.println(factorial(10)); // should be 3628800 StdOut.println(factorial(20)); // watch for overflow. what return type? }
Template / Reference solution
Java test suite See manual	testMain(); test("factorial", 1); test("factorial", 6); test("factorial", 11);
C++ test suite json list of stdin/args tests e.g. `[{"stdin":"hi", "args":["4", "5"]}, {"stdin":"noargs"}]` to just run once with no input use `[{}]`
C++ test suite See manual
Forbidden substrings json list of strings e.g. `["for","while"]`	remove
Solution visibility	remove
Java imports json list of importables e.g. `["java.util.*"]`	remove
Override Java classname else defaults to websheet name	remove
Dependent on other websheets? json list of websheet names in this folder e.g. `["DataStructure"]`	remove
Is example? i.e., just a demo	remove
Add compiler flag(s) json list of flags e.g. `["-Wno-unused-variable"]`	remove
Remove default compiler flag(s) json list of flags see default_cppflags e.g. `["-Wno-write-strings"]`	remove

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