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

示例代码1：

class Solution(object):
    def findString(self, words, s):
        """
        :type words: List[str]
        :type s: str
        :rtype: int
        """
        location = 0
        for i in words:
            if i == s:
                return location
            location += 1
        return -1

示例代码2：

class Solution(object):
    def findString(self, words, s):
        """
        :type words: List[str]
        :type s: str
        :rtype: int
        """
        try:
            res = words.index(s)
        except:
            res = -1
        return res

思路解析：

如果直接return words.index(s)， s不存在时会出错 所以try...except，捕获到错误时，返回-1

示例代码3（二分查找）：

class Solution(object):
    def findString(self, words, s):
        """
        :type words: List[str]
        :type s: str
        :rtype: int
        """
        a, b = 0, len(words) - 1  # 左右指针
        mid = (a+b) // 2  # 初始化
        while a