leetcode1415. The k-th Lexicographical String of All Happy Strings of Length n
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题目如下:
A happy string is a string that:
- consists only of letters of the set
[‘a‘, ‘b‘, ‘c‘]
.s[i] != s[i + 1]
for all values ofi
from1
tos.length - 1
(string is 1-indexed).For example, strings "abc", "ac", "b" and "abcbabcbcb" are all happy strings and strings "aa", "baa" and "ababbc" are not happy strings.
Given two integers
n
andk
, consider a list of all happy strings of lengthn
sorted in lexicographical order.Return the kth string of this list or return an empty string if there are less than
k
happy strings of lengthn
.
Example 1:
Input: n = 1, k = 3 Output: "c" Explanation: The list ["a", "b", "c"] contains all happy strings of length 1. The third string is "c".Example 2:
Input: n = 1, k = 4 Output: "" Explanation: There are only 3 happy strings of length 1.Example 3:
Input: n = 3, k = 9 Output: "cab" Explanation: There are 12 different happy string of length 3 ["aba", "abc", "aca", "acb", "bab", "bac", "bca", "bcb", "cab",
"cac", "cba", "cbc"]. You will find the 9th string = "cab"Example 4:
Input: n = 2, k = 7 Output: ""Example 5:
Input: n = 10, k = 100 Output: "abacbabacb"Constraints:
1 <= n <= 10
1 <= k <= 100
解题思路:n和k都很小,最简单的方法是把所有符合条件的string都求出来,排序后可得到结果。
代码如下:
class Solution(object): def getHappyString(self, n, k): """ :type n: int :type k: int :rtype: str """ queue = [‘a‘,‘b‘,‘c‘] l = [] while len(queue) > 0: item = queue.pop(0) if len(item) == n: l.append(item) continue if item[-1] == ‘a‘: queue.append(item + ‘b‘) queue.append(item + ‘c‘) elif item[-1] == ‘b‘: queue.append(item + ‘a‘) queue.append(item + ‘c‘) elif item[-1] == ‘c‘: queue.append(item + ‘a‘) queue.append(item + ‘b‘) l.sort() if len(l) < k: return ‘‘ return l[k-1]
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