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.

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.

Solution:

1. check substring in string
2. return idx of first substring

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class Solution:
    def strStr(self, haystack: str, needle: str) -> int:
        for i in range((len(haystack) - len(needle) + 1)):
            if haystack[i:i+len(needle)] == needle:
                return i
        return -1

references

• https://leetcode.com/problems/implement-strstr/