https://github.com/dstein64/revdoor
A single-file C++ library for visiting revolving door combinations.
https://github.com/dstein64/revdoor
combinatorics cpp revolving-door taocp
Last synced: about 1 month ago
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A single-file C++ library for visiting revolving door combinations.
- Host: GitHub
- URL: https://github.com/dstein64/revdoor
- Owner: dstein64
- Created: 2020-02-09T22:42:16.000Z (about 5 years ago)
- Default Branch: master
- Last Pushed: 2024-04-30T23:03:10.000Z (about 1 year ago)
- Last Synced: 2025-03-17T17:21:27.992Z (about 2 months ago)
- Topics: combinatorics, cpp, revolving-door, taocp
- Language: C++
- Homepage:
- Size: 26.4 KB
- Stars: 6
- Watchers: 2
- Forks: 1
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
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# revdoor
`revdoor` is a single-file C++ library for visiting *revolving door*
combinations.
The *combinations without replacement* generator implements Algorithm R from
TAOCP 7.2.1.3 [[1]](#references). The *combinations with replacement* generator
implements the same algorithm, modified to support replacement.
The algorithms visit combinations by indicating `in` and `out` swap values for
one or two items on each iteration.
## Quick Start
1. Include the `revdoor.hpp` header.
2. For combinations without replacement, initialize a generator object with
`revdoor::combinations`. For combinations with replacement, initialize a
generator object with `revdoor::combinations_with_replacement`.
3. Use the `state()` method to get the initial state of the generator.
4. Call the `step()` method to proceed to the next combination.
- For combinations without replacement, this takes two `int` pointers:
`out`'s dereference is set to the element that is removed, and `in`'s
dereference is set to the element that is added.
- For combinations without replacement, this takes four `int` pointers:
`out1`'s and `out2`'s dereferences are set to elements that are removed;
`in1`'s and `in2`'s dereferences are set to elements that are added.
In cases where only a single item is swapped out, `*out1 == *in1`.
### Example 1: combinations without replacement
```c++
#include
#include
void process_init_state(const std::vector init_state) { /* ... */ }
void process_change(int out, int in) { /* ... */ }
int main(int argc, char* argv[]) {
int n = 5;
int t = 3;
revdoor::combinations combs(n, t);
std::vector init_state = combs.state();
process_init_state(init_state);
int out, in;
while (combs.step(&out, &in)) {
process_change(out, in);
}
return 0;
}
```
### Example 2: combinations with replacement
```c++
#include
#include
void process_init_state(const std::vector init_state) { /* ... */ }
void process_change(int out, int in) { /* ... */ }
int main(int argc, char* argv[]) {
int n = 5;
int t = 3;
revdoor::combinations_with_replacement combs_rep(n, t);
std::vector init_state = combs_rep.state();
process_init_state(init_state);
int out1, in1, out2, in2;
while (combs_rep.step(&out1, &in1, &out2, &in2)) {
if (out1 != in1)
process_change(out1, in1);
process_change(out2, in2);
}
return 0;
}
```
## Documentation
Refer to the comments in [revdoor.hpp](revdoor.hpp) for detailed information.
## License
The source code has an [MIT License](https://en.wikipedia.org/wiki/MIT_License).
See [revdoor.hpp](revdoor.hpp).
## References
[1] Donald Knuth, The Art of Computer Programming, Volume 4, Fascicle 3: Generating
All Combinations and Partitions (Addison-Wesley Professional, 2005).