permutation.js

process.stdin.resume();
process.stdin.setEncoding('utf8');

permutation = function(ary){
    
    var len = ary.length;
    var perms = [ary];

    for (var startIdx = 0; startIdx <= len-2; startIdx++){
        var tempPerms = [];
    
        perms.forEach(function(perm){
        
            for (var changeIdx = startIdx; changeIdx <= len-1; changeIdx++){
                var tempPerm = perm.slice(0);
            
                var tempVal = tempPerm[startIdx];
                tempPerm[startIdx] = tempPerm[changeIdx];
                tempPerm[changeIdx] = tempVal;
            
                tempPerms.push(tempPerm);
            }  
        
        });
    
        perms = tempPerms.slice(0);
    }
    
    return perms
    
}


// == main == 
console.log(permutation([1,2,3]));

// [ [ 1, 2, 3 ],
//   [ 1, 3, 2 ],
//   [ 2, 1, 3 ],
//   [ 2, 3, 1 ],
//   [ 3, 2, 1 ],
//   [ 3, 1, 2 ] ]