寻找比目标字母大的最小字母

寻找比目标字母大的最小字母

题目:
给你一个排序后的字符列表 letters ，列表中只包含小写英文字母。另给出一个目标字母 target，请你寻找在这一有序列表里比目标字母大的最小字母。

在比较时，字母是依序循环出现的。举个例子：

如果目标字母 target = 'z' 并且字符列表为 letters = ['a', 'b']，则答案返回 'a'

示例：

输入:
letters = ["c", "f", "j"]
target = "a"
输出: "c"

输入:
letters = ["c", "f", "j"]
target = "c"
输出: "f"

输入:
letters = ["c", "f", "j"]
target = "d"
输出: "f"

输入:
letters = ["c", "f", "j"]
target = "g"
输出: "j"

输入:
letters = ["c", "f", "j"]
target = "j"
输出: "c"

输入:
letters = ["c", "f", "j"]
target = "k"
输出: "c

解题思路: 一道搜索左边界的二分题目, 套用模板答题即可

class Solution {
    public char nextGreatestLetter(char[] letters, char target) {
        int l = 0, r = letters.length - 1;
        while(l <= r) {
            int mid = l + (r - l) / 2;
            char ch = letters[mid];
            if(ch < target) {
                l = mid + 1;
            } else if(ch == target) {
                l = mid + 1;
            } else {
                r = mid - 1;
            }
        }
        
        return l == letters.length ? letters[0] : letters[l];
    }
}