# 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().
# Solution
Approach 1: Scan the haystack to match the needle.
# Code (Python)
Approach 1:
class Solution:
def strStr(self, haystack: str, needle: str) -> int:
if not needle:
return 0
for i in range(len(haystack) - len(needle) + 1):
found = True
for j in range(len(needle)):
if haystack[i+j] != needle[j]:
found = False
break
if found:
return i
return -1
# Code (C++)
Approach 1:
class Solution {
public:
int strStr(string haystack, string needle) {
if (needle.size() == 0) return 0;
for (int i = 0; i <= (int)haystack.size() - (int)needle.size(); ++i) // size_t is an unsigned integer.
{
int j = 0;
for (; j < needle.size(); ++j)
{
if (haystack[i+j] != needle[j])
break;
}
if (j == needle.size())
return i;
}
return -1;
}
};