题目
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'.
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"
题解
本题采用二分查找来求解, 转换为查找左边界的二分查找问题. 将目标值加一再在原数组中进行左边界的二分查找, 相当于求解大于给定元素的最小元素.
- class Solution {
- public char nextGreatestLetter(char[] letters, char target) {
- int left = 0;
- int right = letters.length;
- while(left < right){
- int mid = left + (right - left) / 2;
- if(letters[mid] < target + 1){
- left = mid + 1;
- }
- else{
- right = mid;
- }
- }
- return right == letters.length ? letters[0] : letters[right];
- }
- }
来源: http://www.bubuko.com/infodetail-3276004.html