# Leetcode 744. Find Smallest Letter Greater Than Target

## 題解

### 轉 ASCII code + Binary Search

class Solution:
    def nextGreatestLetter(self, letters: List[str], target: str) -> str:
        target = ord(target)
        n = len(letters)
        left = 0
        right = n - 1
        ans = 0
        while left <= right:
            mid = left + (right - left) // 2
            letter = ord(letters[mid])
            if letter <= target:
                left = mid + 1
            elif letter > target:
                ans = mid
                right = mid - 1
        return letters[ans]