cdef class Permute2:

    cdef int n, first
    cdef object lst

    def __init__(self, lst):
        self.lst = lst
        self.first = 0
        self.n = len(lst) - 1

    def __iter__(self):
        return self

    def __next__(self):
        cdef int j, l, k, x, y, z
        if self.first == 0:
            self.first = 1
            return self.lst
        if self.n == 1:
            return [self.lst[1], self.lst[0]]
        while 1:
            if self.lst[-2] < self.lst[-1]:
                self.lst[-2], self.lst[-1] = self.lst[-1], self.lst[-2]
            elif self.lst[-3] < self.lst[-2]:
                if self.lst[-3] < self.lst[-1]:
                    self.lst[-3], self.lst[-2], self.lst[-1] = self.lst[-1], self.lst[-3], self.lst[-2]
                else:
                    self.lst[-3], self.lst[-2], self.lst[-1] = self.lst[-2], self.lst[-1], self.lst[-3]
            else:
                j = self.n - 3
                if j < 0: raise StopIteration
                y = self.lst[j]
                x = self.lst[-3]
                z = self.lst[-1]
                while y >= x:
                    j = j - 1
                    if j < 0: raise StopIteration
                    x = y
                    y = self.lst[j]
                if y < z:
                    self.lst[j] = z
                    self.lst[j+1] = y
                    self.lst[self.n] = x
                else:
                    l = self.n - 1
                    while y >= self.lst[l]:
                        l = l - 1
                    self.lst[j], self.lst[l] = self.lst[l], y
                    self.lst[self.n], self.lst[j+1] = self.lst[j+1], self.lst[self.n]
                k = j + 2
                l = self.n - 1
                while k < l:
                    self.lst[k], self.lst[l] = self.lst[l], self.lst[k]
                    k = k + 1
                    l = l - 1
            return self.lst

var a = ["A", "B", "C", "D"], j = permute(a);
document.write(
    "<h2>", a.join(" - "), " = ", j.length, "</h2>",
    j.join("<br />")
);

//+ Jonas Raoni Soares Silva
//@ http://jsfromhell.com/array/permute [v1.0]

permute = function(v, m){ //v1.0
    for(var p = -1, j, k, f, r, l = v.length, q = 1, i = l + 1; --i; q *= i);
    for(x = [new Array(l), new Array(l), new Array(l), new Array(l)], j = q, k = l + 1, i = -1;
        ++i < l; x[2][i] = i, x[1][i] = x[0][i] = j /= --k);
    for(r = new Array(q); ++p < q;)
        for(r[p] = new Array(l), i = -1; ++i < l; !--x[1][i] && (x[1][i] = x[0][i],
            x[2][i] = (x[2][i] + 1) % l), r[p][i] = m ? x[3][i] : v[x[3][i]])
            for(x[3][i] = x[2][i], f = 0; !f; f = !f)
                for(j = i; j; x[3][--j] == x[2][i] && (x[3][i] = x[2][i] = (x[2][i] + 1) % l, f = 1));
    return r;
};

//+ Jonas Raoni Soares Silva
//@ http://jsfromhell.com/array/permute [v1.0]

permute = function( v, m ){
	for( var j, l = v.length, i = ( 1 << l ) - 1, r = new Array( i ); i; )
		for( r[--i] = [], j = l; j; i + 1 & 1 << --j && ( r[i].push( m ? j : v[j] ) ) );
	return r;
};

document.write( permute( ["A", "B", "C" ], 1 ).join( "<br />" ), "<hr />" );
document.write( permute( ["A", "B", "C" ], 0 ).join( "<br />" ) );