README.md

28. Implement strStr()

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().

Solutions (Python)

1. Linear Scan

class Solution:
    def strStr(self, haystack: str, needle: str) -> int:
        if not needle:
            return 0
        for i in range(len(haystack) - len(needle) + 1):
            flag = True
            for j in range(0, len(needle)):
                if haystack[i + j] != needle[j]:
                    flag = False
                    break
            if flag:
                return i
        return -1