LeetCode 744. 寻找比目标字母大的最小字母

莫名其妙的，LeetCode网站怎么也打不开了。。只好注册了中国版的，中国版里的讨论区好冷清，题解质量也堪忧。

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"

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"

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如果target在数组里的话，找到target最后一次出现的位置，然后向后一步即可

如果target不在数组里的话，最终low的位置就是要返回的元素的位置

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