python全排列和子集

1.全排列

#获取全集
def get_all_set(List,cur=0):
    global result2
    if cur==len(result2) :
        print(result2)
        return
    for each in List:
        if each not in result2[:cur]:#如果下一个元素不在前面已经出现的元素里面
            result2[cur]=each    #把元素加入到result2里面
            get_all_set(List=List,cur=cur+1)#寻找下一个元素

if __name__=='__main__':
    List=['a','b','c','d']
    result2=[None]*len(List)
    get_all_set(List=List)

也可以用python的内置模版itertools解决

from itertools import combinations,permutations

if __name__=='__main__':
    a = ['a', 'b', 'c', 'd']
    print(list(permutations(a, 4)))# 全集

2.子集

#获取List的子集个数
def get_son_set(List):
    global result
    if len(List)<=2:
        return
    for i in range(len(List)):
        first=List[i]
        last=List[:i]+List[i+1:]
        if [first] not in result:
            result.append([first])
        if last not in result:
            result.append(last)
        get_son_set(List=last)

if __name__=='__main__':
    result=[]
    get_son_set(List=[1,2,3,4])
    print(result)

也可以用python的内置模版itertools解决

from itertools import combinations,permutations

if __name__=='__main__':
    for i in range(1,len(a)): #子集
        for each in combinations(a,i):
            print(list(each))

3.实现的思路大致是dfs，理解后不断将问题拆分，调试代码，然后就很容易做出来了