# Question

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().

# Solution

```
class Solution:
def strStr(self, haystack, needle):
"""
:type haystack: str
:type needle: str
:rtype: int
"""
ln = len(needle)
lh = len(haystack)
if ln == 0:
return 0
if lh < ln:
return -1
i = 0
while i <= lh - ln:
if haystack[i] == needle[0] and haystack[i:i+ln] == needle:
return i
i += 1
return -1
```