# Find Smallest Letter Greater Than Target (LeetCode 744)

Circular sorted letters: binary search upper bound, wrap to letters[0].

```python
def nextGreatestLetter(letters, target):
    lo, hi = 0, len(letters)
    while lo < hi:
        m = (lo + hi) // 2
        if letters[m] <= target: lo = m + 1
        else: hi = m
    return letters[lo % len(letters)]
```

Mention wrap-around case in examples. More: [AI tool for job interviews](https://www.linkjob.ai/).

(Affiliation: I work on Linkjob AI.)