Implementation of leetcode question brushing str ()

Realization strStr() function .

Here are two strings haystack and needle , Please come in haystack Find in string needle The first place the string appears （ Subscript from 0 Start ）. If it doesn't exist , Then return to -1 .

explain ：

When needle When it's an empty string , What value should we return ？ This is a good question in an interview .

For this question , When needle When it's an empty string, we should return 0 . This is related to C Linguistic strstr() as well as Java Of indexOf() The definition matches .

Example 1：

Input ：haystack = “hello”, needle = “ll”
Output ：2
Example 2：

Input ：haystack = “aaaaa”, needle = “bba”
Output ：-1
Example 3：

Input ：haystack = “”, needle = “”
Output ：0

Tips ：

1 <= haystack.length, needle.length <= 104
haystack and needle It only consists of lowercase English characters

source ： Power button （LeetCode）
link ：https://leetcode-cn.com/problems/implement-strstr

var strStr = function(haystack, needle) {
    
  need_length = needle.length
  if (need_length === 0) return 0
  if (need_length > haystack.lenght) return -1
  let start = 0, end = 0
  for (let k in haystack) {
    
    k = parseInt(k)
    start = k
    end = k + need_length
    if (haystack.slice(start, end) == needle) {
    
      return start
    }
  }
  return -1
}

let haystack = "", needle = ""

res = strStr(haystack, needle)

console.log(res);