从Python中的排列中查找Palidrome

import itertools

def is_palindrome(s):
    return s == s[::-1]

def find_palindromic_permutations(input_string):
    palindromic_permutations = set()
    for perm in itertools.permutations(input_string):
        perm_str = ''.join(perm)
        if is_palindrome(perm_str):
            palindromic_permutations.add(perm_str)
    return palindromic_permutations

# 示例使用
input_str = "aabb"
palindromes = find_palindromic_permutations(input_str)
print("Palindromic permutations of", input_str, "are:", palindromes)

def find_palindromic_permutations_optimized(input_string):
    from collections import Counter
    char_count = Counter(input_string)
    odd_count = sum(1 for count in char_count.values() if count % 2 != 0)
    
    if len(input_string) % 2 == 0 and odd_count != 0:
        return set()  # 偶数长度字符串不能有奇数次字符
    if len(input_string) % 2 != 0 and odd_count != 1:
        return set()  # 奇数长度字符串只能有一个奇数次字符
    
    half_string = ''.join([char * (count // 2) for char, count in char_count.items()])
    palindromic_permutations = set()
    
    for perm in itertools.permutations(half_string):
        half_str = ''.join(perm)
        full_str = half_str + half_str[::-1]
        if len(input_string) % 2 != 0:
            for char in char_count:
                if char_count[char] % 2 != 0:
                    full_str = full_str[:len(full_str)//2] + char + full_str[len(full_str)//2:]
                    break
        if is_palindrome(full_str):
            palindromic_permutations.add(full_str)
    
    return palindromic_permutations

# 示例使用
input_str = "aabb"
palindromes = find_palindromic_permutations_optimized(input_str)
print("Optimized Palindromic permutations of", input_str, "are:", palindromes)