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Tested Python solution for LeetCode 267 with 15 pytest cases. Generate a practice environment with lcpy.
lcpy gen -n 267 # by problem number
lcpy gen -s palindrome_permutation_ii # by problem name
s, return all the palindromic permutations (without duplicates) of it.
You may return the answer in any order. If s has no palindromic permutation, return an empty list.
Input: s = "aabb"
Output: ["abba","baab"]
Input: s = "abc"
Output: []
1 <= s.length <= 16s consists of only lowercase English letters.from collections import Counter
class Solution:
# Time: O(n * (n/2)!) for generating each half permutation
# Space: O(n)
def generate_palindromes(self, s: str) -> list[str]:
counts = Counter(s)
mid = ""
for char, count in counts.items():
if count % 2:
if mid:
return []
mid = char
counts[char] -= 1
results: list[str] = []
def build(current: str) -> None:
if all(value == 0 for value in counts.values()):
results.append(current)
return
for char in counts:
if counts[char] > 0:
counts[char] -= 2
build(char + current + char)
counts[char] += 2
build(mid)
return results
| Time | Space |
|---|---|
| O(n * (n/2)!) for generating each half permutation | O(n) |