index.js

// Implement strStr().
// Return the index of the first occurrence of needle in haystack, or - 1 if needle is not part of haystack.

// Example 1:

// Input: haystack = "hello", needle = "ll"
// Output: 2
// Example 2:

// Input: haystack = "aaaaa", needle = "bba"
// Output: -1
// 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().

// Constraints:

// haystack and needle consist only of lowercase English characters.

// Solution

const strStr = (haystack, needle) => {
    if (!needle.length) {
        return 0;
    }

    for (let i = 0; i < haystack.length; i++) {
        if (haystack[i] === needle[0]) {
            if (haystack.slice(i, i + needle.length) === needle) {
                return i;
            }
        }
    }

    return -1;
};