> For the complete documentation index, see [llms.txt](https://jaywin.gitbook.io/leetcode/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://jaywin.gitbook.io/leetcode/solutions/1415-the-k-th-lexicographical-string-of-all-happy-strings-of-length-n.md).

# 1415. The k-th Lexicographical String of All Happy Strings of Length n

<https://leetcode.com/problems/the-k-th-lexicographical-string-of-all-happy-strings-of-length-n>

## Description

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 of `i` from `1` to `s.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` and `k`, consider a list of all happy strings of length `n` 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 length `n`.

**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`

&#x20;

## ac

```java
```