Permutation -- Liet Ke Hoan vi

def lietkehoanvi(arr, output=[]):
    for i in arr:
        if i not in output:
            output.append(i)
            if len(output) == len(arr):
                print output
            else:
                lietkehoanvi(arr, output)
            output.pop()

lietkehoanvi([1,2,3,4])

---------------------------


for i in [x*x for x in range(1,6)]:
    print i

for i in (x*x for x in range(1,6)):
    print i

def generator():
    for i in range(1,6):
        yield i*i

for i in generator():
    print i

-------------------------------------

class HoanVi():
    def __init__(self, data):
        self._data = data
        self._out = []
   
    def __iter__(self):
        return self.next()

    def next(self):
        for i in self._data:
            if i not in self._out:
                self._out.append(i)
                if len(self._out) == len(self._data):
                    yield self._out
                else:
                    for v in self.next():
                        yield v
                self._out.pop()

for i in HoanVi([1,2,3,4]):
    print i

------------------------



import copy


class HoanVi():
    _data = []
    _result = []
    _out = []
   
       
    def __init__(self, arr):
        self._data = arr[:]
        self.hoanvi()
       
    def hoanvi(self):
        for i in self._data:
            if i not in self._out:
                self._out.append(i)
                if len(self._out) == len(self._data):
                    a = copy.copy(self._out)
                    self._result.append(a)
                else:
                    self.hoanvi()
                self._out.pop()
   
   
a = HoanVi([1,5,3,6])
for i in a._result:
    print i

-------------------------

[1, 5, 3, 6]

[1, 5, 6, 3]

[1, 3, 5, 6]

[1, 3, 6, 5]

[1, 6, 5, 3]

[1, 6, 3, 5]

[5, 1, 3, 6]

[5, 1, 6, 3]

[5, 3, 1, 6]

[5, 3, 6, 1]

[5, 6, 1, 3]

[5, 6, 3, 1]

[3, 1, 5, 6]

[3, 1, 6, 5]

[3, 5, 1, 6]

[3, 5, 6, 1]

[3, 6, 1, 5]

[3, 6, 5, 1]

[6, 1, 5, 3]

[6, 1, 3, 5]

[6, 5, 1, 3]

[6, 5, 3, 1]

[6, 3, 1, 5]

[6, 3, 5, 1]