heaps-permute


A JavaScript implementation of Heap's efficient Permutation Algorithm.

This algorithm is "efficient", but still runs in factorial time. It will probably run out of memory if you try it on an array longer than 10 items. For example:

- n = 7 will finish within 5 milliseconds (5040 permutations)
- n = 8 will finish within 50 milliseconds (40,320 permutations)
- n = 9 will finish within 500 milliseconds (362,880 permutations)
- n = 10 will finish within 6000 milliseconds (328,800 permutations)

Install

``
$ npm install heaps-permute
`

`js
var permute = require('heaps-permute');
`

Usage

$3

This returns all the permutations for the given array.

`js
permute([1, 2, 3]);

// returns
[
[ 1, 2, 3 ],
[ 2, 1, 3 ],
[ 3, 1, 2 ],
[ 1, 3, 2 ],
[ 2, 3, 1 ],
[ 3, 2, 1 ]
];


permute(['a', 'b', 'c', 'd'])

// returns
[
[ 'a', 'b', 'c', 'd' ],
[ 'b', 'a', 'c', 'd' ],
[ 'c', 'a', 'b', 'd' ],
[ 'a', 'c', 'b', 'd' ],
[ 'b', 'c', 'a', 'd' ],
[ 'c', 'b', 'a', 'd' ],
[ 'd', 'b', 'c', 'a' ],
[ 'b', 'd', 'c', 'a' ],
[ 'c', 'd', 'b', 'a' ],
[ 'd', 'c', 'b', 'a' ],
[ 'b', 'c', 'd', 'a' ],
[ 'c', 'b', 'd', 'a' ],
[ 'd', 'a', 'c', 'b' ],
[ 'a', 'd', 'c', 'b' ],
[ 'c', 'd', 'a', 'b' ],
[ 'd', 'c', 'a', 'b' ],
[ 'a', 'c', 'd', 'b' ],
[ 'c', 'a', 'd', 'b' ],
[ 'd', 'a', 'b', 'c' ],
[ 'a', 'd', 'b', 'c' ],
[ 'b', 'd', 'a', 'c' ],
[ 'd', 'b', 'a', 'c' ],
[ 'a', 'b', 'd', 'c' ],
[ 'b', 'a', 'd', 'c' ]
];
`

$3

This method invokes cb each time a unique permutation is found. The new permutation will be the only argument to the callback.

`js
permute.callback([1, 2, 3], console.log);

// will print to the console:

[ 1, 2, 3 ]
[ 2, 1, 3 ]
[ 3, 1, 2 ]
[ 1, 3, 2 ]
[ 2, 3, 1 ]
[ 3, 2, 1 ]
`

Do not pass this method a third argument: it's needed for an internal counter.

Tests

To run the test suite, first install the dependencies, then run npm test:

`
$ npm install
$ npm test
`

To test code coverage:

`
$ npm run cover
``