CODEWITHSUNDEEP
pythonalgorithmyield
zangw
zangw

Reputation: 48356

Python yield statement issue in recursive function?

Now, I learn to how to use yield in python program. so I want to implement word permutation in python.

def permuteArr(arr, index=0):
    '''(list, int) -> list

    Get all the permutation of the elements in list.
    >>> arr = ['a', 'b', 'c']
    >>> for val in permuteArr(arr):
            print val
    '''
    if index == len(arr):
        yield arr
    else:
        for idx in range(index, len(arr)):
            arr[idx], arr[index] = arr[index], arr[idx]
            for val in permuteArr(arr, idx+1):
                yield val
            arr[idx], arr[index] = arr[index], arr[idx]

if '__name__' == '__main__':
    arr = ['a', 'b', 'c']
    for val in permuteArr(arr, 0):
        print val

However, I run it in python shell under window, the results are not correct. There are only four results.

>>> for v in permuteArr(['a', 'b', 'c']):
    print v

['a', 'b', 'c']
['a', 'c', 'b']
['b', 'a', 'c']
['c', 'b', 'a']

Is anything wrong when I use yield or in my program?

Upvotes: 1

Views: 153

Answers (1)

mr0re1
mr0re1

Reputation: 1585

In loop for val in permuteArr(arr, idx+1): replace idx + 1 on index + 1

Upvotes: 2

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