编程题10

给定一个只包含小写字母的有序数组letters 和一个目标字母 target，寻找有序数组里面比目标字母大的最小字母。
数组里字母的顺序是循环的。举个例子，如果目标字母target = ‘z’ 并且有序数组为 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”
class Solution {
public char nextGreatestLetter(char[] letters, char target) {
int left = 0;
int right = letters.length-1;
if (target >= letters[right]) {
return letters[0];
}
while (left < right) {
int mid =(left + right) / 2;
if (target >= letters[mid]) {
left = mid + 1;
}
else {
right = mid;
}
}
return letters[left];
}
}