> For the complete documentation index, see [llms.txt](https://rachel2011.gitbook.io/leetcode_cc150/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://rachel2011.gitbook.io/leetcode_cc150/binary-search/744.-find-smallest-letter-greater-than-target.md).

# 744. Find Smallest Letter Greater Than Target

Given a list of sorted characters `letters` containing only lowercase letters, and given a target letter `target`, find the smallest element in the list that is larger than the given target.

Letters also wrap around. For example, if the target is `target = 'z'` and `letters = ['a', 'b']`, the answer is `'a'`.

**Examples:**<br>

```
Input:
letters = ["c", "f", "j"]
target = "a"
Output: "c"

Input:ji
letters = ["c", "f", "j"]
target = "c"
Output: "f"

Input:
letters = ["c", "f", "j"]
target = "d"
Output: "f"

Input:
letters = ["c", "f", "j"]
target = "g"
Output: "j"

Input:
letters = ["c", "f", "j"]
target = "j"
Output: "c"

Input:
letters = ["c", "f", "j"]
target = "k"
Output: "c"
```

**Note:**<br>

1. `letters` has a length in range `[2, 10000]`.
2. `letters` consists of lowercase letters, and contains at least 2 unique letters.
3. `target` is a lowercase letter.

解法：

用二分查找

```
class Solution(object):
    def nextGreatestLetter(self, letters, target):
        """
        :type letters: List[str]
        :type target: str
        :rtype: str
        """
        # l = [char for char in letters if char> target]
        # return min(l) if len(l) >0 else letters[0]
        l = 0
        r = len(letters) - 1
        while l <= r:
            m = l + (r - l) / 2
            if letters[m] <= target:
                l = m + 1
            else:
                r = m - 1
        if l < len(letters):
            return letters[l]
        else:
            return letters[0]

```