Word Permutations

permutations.js

// To run with node: npm install lodash && node perms.js star
var _ = require('lodash'),
    words = ['stars'];

function getPermutations(word) {
    // Stop case for single character
    if (word.length === 1) {
        return [word];
    }

    // For each letter...
    return _.reduce(word, function (result, letter, idx) {
        // Grab the other letters
        var rest = [word.slice(0, idx), word.slice(idx + 1)].join(''),
            // Get all permutations of the other letters to the right
            rightCombos = getPermutations(rest);
        
        // For each right combo, add the current letter onto it and
        // push into result
        _.each(rightCombos, function (combo) {
            result.push(letter + combo);
        });

        // Return the aggregated results from all letter combinations
        return result;
    }, []);
}


// Allow passing in words to do
if (process.argv.length > 2) {
    words = process.argv.slice(2);
}

_.each(words, function (word) {
    var perms = _.unique(getPermutations(word)),
        title = word + ' (' + perms.length + ')';

    console.log(title);
    console.log(new Array(title.length + 1).join('='));

    _.each(perms, function (perm) {
        console.log(perm);
    });
    console.log('');
});

Bugged me all weekend /cc @zpao