744.find-smallest-letter-greater-than-target.cpp

/*
 * @lc app=leetcode id=744 lang=cpp
 *
 * [744] Find Smallest Letter Greater Than Target
 *
 * https://leetcode.com/problems/find-smallest-letter-greater-than-target/description/
 *
 * algorithms
 * Easy (44.31%)
 * Likes:    234
 * Dislikes: 362
 * Total Accepted:    44.7K
 * Total Submissions: 100.9K
 * Testcase Example:  '["c","f","j"]\n"a"'
 *
 * 
 * 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:
 * 
 * letters has a length in range [2, 10000].
 * letters consists of lowercase letters, and contains at least 2 unique
 * letters.
 * target is a lowercase letter.
 * 
 * 
 */
class Solution {
public:
    char nextGreatestLetter(vector<char>& letters, char target) {
        int n = letters.size();
        
        // if((int)letters[n-1] < (int)target)
        //     return letters[0];
        int pos = -1;
        for(int k=n; k>=1; k/=2)
            while(pos+k<n && (int)letters[pos+k] <= (int)target)
                pos += k;
        return letters[(pos+1)%n];
    }
};