# 744. Find Smallest Letter Greater Than Target

### Approach 1: Binary Search using `bisect`

```python
class Solution(object):
    def nextGreatestLetter(self, letters, target):
        """
        :type letters: List[str]
        :type target: str
        :rtype: str
        """
        index = bisect.bisect(letters, target)
        return letters[index % len(letters)]
```

As the documentation of bisect reads, bisect.bisect returns an insertion point which comes after (to the right of) any existing entries of target in letters

> `bisect.bisect`(*a*, *x*, *lo=0*, *hi=len(a)*)
>
> > Similar to [`bisect_left()`](https://docs.python.org/3.6/library/bisect.html#bisect.bisect_left), but returns an insertion point which comes after (to the right of) any existing entries of *x* in *a*.
> >
> > The returned insertion point *i* partitions the array *a* into two halves so that `all(val <= x for valin a[lo:i])` for the left side and `all(val > x for val in a[i:hi])` for the right side.

This algorithm comes in at 100% percentile runtime

> **Time Complexity:** *O(logN),* because it uses a basic bisection
>
> **Space Complexity:** *O(1)*