Formatted question description: https://leetcode.ca/all/744.html

# 744. Find Smallest Letter Greater Than Target (Easy)

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.

## Solution 1.

// OJ: https://leetcode.com/problems/find-smallest-letter-greater-than-target/

// Time: O(NlogN)
// Space: O(1)
class Solution {
public:
char nextGreatestLetter(vector<char>& letters, char target) {
auto i = upper_bound(letters.begin(), letters.end(), target);
return i == letters.end() ? letters : *i;
}
};


Java

class Solution {
public char nextGreatestLetter(char[] letters, char target) {
int length = letters.length;
char lastLetter = letters[length - 1];
if (lastLetter <= target)
return letters;
int index = binarySearch(letters, target);
return letters[index];
}

public int binarySearch(char[] letters, char target) {
target++;
int low = 0, high = letters.length - 1;
while (low <= high) {
int mid = (high - low) / 2 + low;
char c = letters[mid];
if (c == target)
return mid;
else if (c > target)
high = mid - 1;
else
low = mid + 1;
}
return low;
}
}