# Leetcode: Find Smallest Letter Greater Than Target

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:

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

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.

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.

```## Blog link: https://code.dennyzhang.com/find-smallest-letter-greater-than-target
## Basic Ideas: Binary search
##  Assumption: duplicate characters
##              ["a", "a", "b"], "c"
## Complexity: Time O(log(n)), Space O(1)
class Solution(object):
def nextGreatestLetter(self, letters, target):
"""
:type letters: List[str]
:type target: str
:rtype: str
"""
length = len(letters)
left, right = 0, length - 1
while left <= right:
mid = left + (right-left)/2
if letters[mid] == target:
break
elif letters[mid] > target:
right = mid - 1
else:
left = mid + 1

if left <= right:
# It has target inside, now find the last element equals the target
left, right = 0, length - 1
while left < right:
mid = left + (right-left)/2
if letters[mid] > target:
right = mid - 1
else:
left = mid
if right - left == 1:
if letters[right] == target:
left = right
break
else:
break
index = (left + 1) % length
return letters[index]
else:
# It doesn't have the target
# ['a', 'a', 'a', 'a', 'c', 'c'], 'b'
index = (right + 1) % length
return letters[index]

# s = Solution()
# print s.nextGreatestLetter(["c","f","j"], "j")
```

Share It, If You Like It.