手工python怎么写全排列？

Question

不用iteraltools的permutation

symbol=["A","B","C"]
rst=[]
for i in symbol:
    for j in symbol:
        for k in symbol:
            rst.append([i,j,k])
print(rst)#生成排列

如果有N=10层,就很难写10个for循环了。应该怎样办呢？

Answer 1

可以考虑用递归啊，循环加递归即可。
比如：

rst=[]
symbol=["A","B","C","D","E","F","G","H","I","J"]
def perm(n,b,e):
    if b>=e :
        rst.append(n)
    else:
        i = b
        for num in range(b, e):
            n[num],n[i] = n[i],n[num]
            perm(n,b+1,e)
            n[num],n[i]=n[i],n[num]
perm(symbol, 0, len(symbol) )
print(rst)