反转Python中的排列 [英] Inverting permutations in Python

问题描述

我是编程新手，我正在尝试编写Python函数，以使用以下代码在{1,2,3，...，n}上查找排列的逆:

I'm new to programming, and I'm trying to write a Python function to find the inverse of a permutation on {1,2,3,...,n} using the following code:

def inv(str):
    result = []
    i = list(str).index(min(list(str)))
    while min(list(str)) < len(list(str)) + 1:
        list(str)[i : i + 1] = [len(list(str)) + 1]
        result.append(i + 1)
    return result

但是，当我尝试使用该函数时，inv('<mypermutation>')返回[].我想念什么吗? Python是否由于某种语法原因跳过了我的while循环?我在Google和stackoverflow上搜索的主题都没有返回任何有用的信息.

However, when I try to use the function, inv('<mypermutation>') returns []. Am I missing something? Is Python skipping over my while loop for some syntactical reason I don't understand? None of my google and stackoverflow searches on topics I think of are returning anything helpful.

推荐答案

如果只需要逆排列，则可以使用

If you only want the inverse permutation, you can use

def inv(perm):
    inverse = [0] * len(perm)
    for i, p in enumerate(perm):
        inverse[p] = i
    return inverse

perm = [3, 0, 2, 1]
print(inv(perm))
for i in perm:
    print(inv(perm)[i])

[1, 3, 2, 0]
0
1
2
3

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