javascript permutation generator with permutation length parameter
javascript, node.js, permutation
Solution
You can imagine the length as representing the number of slots. Each slot has N possibilities, given that N is the number of elements in your initial list. So given three values `[1,2,3]`, you will have a total of `3 x 3 x 3 = 27` permutations.
Here's my attempt. Comments included!
var list = [1,2,3];
var getPermutations = function(list, maxLen) {
// Copy initial values as arrays
var perm = list.map(function(val) {
return [val];
});
// Our permutation generator
var generate = function(perm, maxLen, currLen) {
// Reached desired length
if (currLen === maxLen) {
return perm;
}
// For each existing permutation
for (var i = 0, len = perm.length; i < len; i++) {
var currPerm = perm.shift();
// Create new permutation
for (var k = 0; k < list.length; k++) {
perm.push(currPerm.concat(list[k]));
}
}
// Recurse
return generate(perm, maxLen, currLen + 1);
};
// Start with size 1 because of initial values
return generate(perm, maxLen, 1);
};
var res = getPermutations(list, 3);
console.log(res);
console.log(res.length); // 27
fiddle
Problem
I've seen a few generators out there but they all make a squared matrix. For example, you give it a list of three items and it'll assume the output of the length is also three. However, I'd like to specify the items and the length. Sound like an easy problem can't believe there isn't a library available for it. Would like to avoid writing this myself if there's a tested library out there. Any suggestions would be great. Example of what i've found ``` var list = 'abc'; perms = permutations(list); //you cannot define the length ``` Example ``` var list = 'abc'; var length = 3; perms = permutations(list,length); console.log(perms); /* output a,a,a a,b,c a,b,a a,c,a c,a,a ... */ ``` I would like to be able to change length and should create permutations accordingly ``` length = 2 a,a a,b b,b b,a length = 4 a,a,a,a a,a,a,b .... ```