744. Find Smallest Letter Greater Than Target

/***************************************************

You are given an array of characters letters that is sorted in non-decreasing order, and a character target. There are at least two different characters in letters.

Return the smallest character in letters that is lexicographically greater than target. If such a character does not exist, return the first character in letters.

 

Example 1:

Input: letters = ["c","f","j"], target = "a"
Output: "c"
Explanation: The smallest character that is lexicographically greater than 'a' in letters is 'c'.
Example 2:

Input: letters = ["c","f","j"], target = "c"
Output: "f"
Explanation: The smallest character that is lexicographically greater than 'c' in letters is 'f'.
Example 3:

Input: letters = ["x","x","y","y"], target = "z"
Output: "x"
Explanation: There are no characters in letters that is lexicographically greater than 'z' so we return letters[0].
 

Constraints:

2 <= letters.length <= 104
letters[i] is a lowercase English letter.
letters is sorted in non-decreasing order.
letters contains at least two different characters.
target is a lowercase English letter.

************************************************

class Solution {
public:
    char nextGreatestLetter(vector<char>& letters, char target) {
       int s=0; int e=letters.size()-1;
       int res=-1;
       while(s<=e){
           int mid=s+(e-s)/2;
           if(letters[mid]>target){
               res=mid;
               e=mid-1;
           }
           else{
               s=mid+1;
           }
       } 
       if(res==-1){
           res=0;
       }
       return letters[res];
    }
};