干丫的算法之稀疏数组搜索（4）

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leetcode 面试题10.05

题目

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

解析

注意审题，稀疏数组是已排好序的，找某个的最优方法就是二分查找

参考代码

/**
 * @param {string[]} words
 * @param {string} s
 * @return {number}
 */
var findString = function(words, s) {
    if (words === null || words.length === 0) return -1;
	
	let left = 0;
	let right = words.length - 1;
	while (left <= right) {
	    while (words[left] === '') left++;
	    while (words[right] === '') right--;
	    let mid = left + Math.floor((right - left) / 2);

	    while (words[mid] === '' && mid < right) mid++;

	    if (words[mid] === s) return mid;

	    // 根据第一个不同的字符的ascii值码进行比较
	    if (s < words[mid]) {
	        right = mid - 1;
	    } else {
	        left = mid + 1;
	    }
	}
	
	return -1;
};