cpp/recursion/bin_combo

Viewing cpp/recursion/bin_combo_str by redekopp@usc.edu. You have unsaved changes. Log in above to create, edit, preview and publish Websheets.

Property Value

Description
html markup
shown to student

Complete the following program to print out all possible binary combinations
of a given number of digits. E.g. <tt>./bincombos</tt> with input <tt>1</tt>
should print out
<pre>
0
1
</pre>
With input 2 it should print out
<pre>
00
01
10
11
</pre>
where the bold/italics is added just to show the relation to the previous case (don't try to add it).
With input 3 it should likewise print out
<pre>
000
001
010
011
100
101
110
111
</pre>
To do this,
fill out the recursive function
<tt>void bincombos(string prefix, int len)</tt>.
It should try appending a '0' or '1' to the prefix in turn,
using recursion to go through
all the options of the remaining bits. For instance when n=2,
you want the recursive call tree to look like this:
<pre>
("", 2)
/ \
("0", 2) ("1", 2)
/ \ / \
("00", 2) ("01", 2) ("10", 2) ("11", 2)
</pre>
so it will print out
<pre>
00
01
10
11
</pre>

Epilogue
html markup
shown when solved

remove
Public permissions remove
Remarks
Comments, history, license, etc.

Originally by Mark Redekopp (redekopp@usc.edu) and Dave Pritchard (daveagp@gmail.com)

remove
Engine
Choices
json list of string, bool pairs
e.g. [["good", true], ["bad", false]]

Correct answer
Template / Reference solution

Template / Reference solution

#include <iostream>
using namespace std;

void bincombos(string prefix, int len) {
// base case: we don't have to add any more 0s and 1s
// the prefix is a complete string, so print it and quit
\[
if (prefix.length() == len) {
cout << prefix << endl;
return;
}
]\

// recursive case: try adding 0 or 1 as the next digit,
// then continue trying all possibilities after that
\[
bincombos(prefix + "0", len);
bincombos(prefix + "1", len);
]\
}

int main() {
// what size combos do we want?
int numBits;
cin >> numBits;

// start the recursion
\[
bincombos("", numBits);
]\

return 0;
}

Java test suite
See manual

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 [{}]

[
{"stdin": "0"},
{"stdin": "1"},
{"stdin": "2"},
{"stdin": "3"}
]

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

Property	Value
Description html markup shown to student	Complete the following program to print out all possible binary combinations of a given number of digits. E.g. <tt>./bincombos</tt> with input <tt>1</tt> should print out <pre> 0 1 </pre> With input 2 it should print out <pre> 0<b>0</b> 0<b>1</b> 1<i>0</i> 1<i>1</i> </pre> where the bold/italics is added just to show the relation to the previous case (don't try to add it). With input 3 it should likewise print out <pre> 0<b>00</b> 0<b>01</b> 0<b>10</b> 0<b>11</b> 1<i>00</i> 1<i>01</i> 1<i>10</i> 1<i>11</i> </pre> To do this, fill out the recursive function <tt>void bincombos(string prefix, int len)</tt>. It should try appending a '0' or '1' to the prefix in turn, using recursion to go through all the options of the remaining bits. For instance when n=2, you want the recursive call tree to look like this: <pre> ("", 2) / \ ("0", 2) ("1", 2) / \ / \ ("00", 2) ("01", 2) ("10", 2) ("11", 2) </pre> so it will print out <pre> 00 01 10 11 </pre>
Epilogue html markup shown when solved	remove
Public permissions	remove
Remarks Comments, history, license, etc.	Originally by Mark Redekopp (redekopp@usc.edu) and Dave Pritchard (daveagp@gmail.com) remove
Engine
Choices json list of string, bool pairs e.g. `[["good", true], ["bad", false]]`
Correct answer
Template / Reference solution
Template / Reference solution	#include <iostream> using namespace std; void bincombos(string prefix, int len) { // base case: we don't have to add any more 0s and 1s // the prefix is a complete string, so print it and quit \[ if (prefix.length() == len) { cout << prefix << endl; return; } ]\ // recursive case: try adding 0 or 1 as the next digit, // then continue trying all possibilities after that \[ bincombos(prefix + "0", len); bincombos(prefix + "1", len); ]\ } int main() { // what size combos do we want? int numBits; cin >> numBits; // start the recursion \[ bincombos("", numBits); ]\ return 0; }
Java test suite See manual
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 `[{}]`	[ {"stdin": "0"}, {"stdin": "1"}, {"stdin": "2"}, {"stdin": "3"} ]
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

Optional properties:

Note: problems are open-source by default (see 'Public permissions'). Assumed license for open problems is Creative Commons 4.0 Attribution-ShareAlike unless specified in 'Remarks'.