Offer Penalty for prove safety (xxvii): alignment of the string

Offer Penalty for prove safety (xxvii): alignment of the string

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First, the primer

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Second, the title

A string input, prints out all permutations of the characters in the string in lexicographic order. For example input string abc, abc print all strings of characters a, b, c can be arranged out, acb, bac, bca, cab and cba.

Enter a description:

Enter a string of not more than 9 (possibly repeated characters), characters include only lowercase letters.

1, ideas

Recursion, the first fixed problem into the first character, the remaining characters are arranged request; when evaluated with the remaining characters are arranged as the original problem.

(1) traverse all possible position appears in the first character (ie: the first character sequentially exchanged with all subsequent characters);

(2) fixing the first character, character seeking arranged behind (i.e.: during traversal of Step 1, insert implemented recursively).

2, programming

python

Code implementation:

# -*- coding:utf-8 -*-
class Solution:
    def Permutation(self, ss):
        # write code here
        if len(ss) <=1:
            return ss
        res = set()
        #  遍历字符串，固定第一个元素，第一个元素可以取a,b,c...，然后递归求解
        for i in range(len(ss)):
            # 使用排序算法 字符串是除了固定的那个字符 依次固定了元素，其他的全排列（递归求解）
            for j in self.Permutation(ss[:i] + ss[i+1:]):
                # 集合添加元素的方法add(),集合添加去重（若存在重复字符，排列后会存在相同，如baa,baa）
                res.add(ss[i] + j)
        # sorted()能对可迭代对象进行排序,结果返回一个新的list
        return sorted(res)

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