python使用递归解决全排列数字示例

第一种方法:递归

复制代码 代码如下:

def perms(elements):
    if len(elements) <=1:
        yield elements
    else:
        for perm in perms(elements[1:]):
            for i in range(len(elements)):
                yield perm[:i] + elements[0:1] + perm[i:]

for item in list(perms([1, 2, 3,4])):
    print item


结果
复制代码 代码如下:

[1, 2, 3, 4]
[2, 1, 3, 4]
[2, 3, 1, 4]
[2, 3, 4, 1]
[1, 3, 2, 4]
[3, 1, 2, 4]
[3, 2, 1, 4]
[3, 2, 4, 1]
[1, 3, 4, 2]
[3, 1, 4, 2]
[3, 4, 1, 2]
[3, 4, 2, 1]
[1, 2, 4, 3]
[2, 1, 4, 3]
[2, 4, 1, 3]
[2, 4, 3, 1]
[1, 4, 2, 3]
[4, 1, 2, 3]
[4, 2, 1, 3]
[4, 2, 3, 1]
[1, 4, 3, 2]
[4, 1, 3, 2]
[4, 3, 1, 2]
[4, 3, 2, 1]

第二种方法:python标准库

复制代码 代码如下:

import itertools
print list(itertools.permutations([1, 2, 3,4],3))

源代码如下:

复制代码 代码如下:

#coding:utf-8
import itertools
print list(itertools.permutations([1, 2, 3,4],3))

def perms(elements):
    if len(elements) <=1:
        yield elements
    else:
        for perm in perms(elements[1:]):
            for i in range(len(elements)):
                yield perm[:i] + elements[0:1] + perm[i:]

for item in list(perms([1, 2, 3,4])):
    print item

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