## Description

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

### 1. Array

# Time: O(mn)
# Space: O(1)
class Solution:
def strStr(self, haystack: str, needle: str) -> int:
if not needle:
return 0
h = len(haystack)
n = len(needle)
if h < n:
return -1
for i in range(h - n + 1):
if haystack[i] == needle[0]:
idx = i
j = 0
while j < n:
if haystack[idx] != needle[j]:
break
j += 1
idx += 1
if j == n:
return i
return -1

# 74/74 cases passed (36 ms)
# Your runtime beats 37.85 % of python3 submissions
# Your memory usage beats 100 % of python3 submissions (12.7 MB)