leetcode 面试题 10.05. 稀疏数组搜索

稀疏数组搜索。有个排好序的字符串数组，其中散布着一些空字符串，编写一种方法，找出给定字符串的位置。

示例1:

输入: words = ["at", "", "", "", "ball", "", "", "car", "", "","dad", "", ""], s = "ta"
输出：-1
说明: 不存在返回-1。
示例2:

输入：words = ["at", "", "", "", "ball", "", "", "car", "", "","dad", "", ""], s = "ball"
输出：4
提示:

words的长度在[1, 1000000]之间

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/sparse-array-search-lcci
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采用二分法，若是遇到空字符串则往前寻找，若前面都是空字符串，则往后面寻找。

    public int findString(String[] words, String s) {
        int st = 0;
        int end = words.length - 1;
        while (st <= end) {
            int m = st + ((end - st) >> 1);
            while ("".equals(words[m])) {
                m++;
                if (m > end) {
                    m = st + ((end - st) >> 1);
                    while ("".equals(words[m])) {
                        m--;
                        if (m < st) {
                            return -1;
                        }
                    }
                }
            }
            if (words[m].compareTo(s) == 0) {
                return m;
            }
            if (words[m].compareTo(s) > 0) {
                end = m - 1;
            } else {
                st = m + 1;
            }
        }
        return -1;
    }