28. Implement strStr() - 《leetcode》

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()).

Runtime: 52 ms, faster than 100.00% of JavaScript online submissions for Implement strStr().

/**
 * @param {string} haystack
 * @param {string} needle
 * @return {number}
 */
var strStr = function(haystack, needle) {
    if (!needle) {
        return 0;
    }
    const needleLen = needle.length;
    const haystackLen = haystack.length;
    const end = haystackLen - needleLen;
    for (let i = 0; i <= end; i++) {
        if (haystack.substring(i, i + needleLen) === needle) {
            return i;
        }
    }
    return -1;
};