Description
Implement strStr().
Return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.
Clarification:
What should we return when needle is an empty string? This is a great question to ask during an interview.
For the purpose of this problem, we will return 0 when needle is an empty string. This is consistent to C's strstr() and Java's indexOf().
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
Constraints:
0 <= haystack.length, needle.length <= 5 * 104
haystack and needle consist of only lower-case English characters.
Thinking
- traverse the haystack string, find out if there is the one letter equal the first letter in the needle string
- if true, we can slice the length that equal to the needle string from the letter we found in the haystack, compare them
- if equal the index
- otherwise, we always return -1
/**
* @param {string} haystack
* @param {string} needle
* @return {number}
*/
let strStr = (haystack, needle) => {
if (needle.length === 0) return 0
let initial = needle[0]
for (let i = 0; i < haystack.length; i++) {
if (haystack[i] === initial) {
if (haystack.slice(i, (i + needle.length)) === needle) {
return i
}
}
}
return -1
}