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# Implement strStr() LeetCode Solution

## Problem – Implement strStr()

Implement strStr().

Given two strings `needle` and `haystack`, 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``````

Constraints:

• `1 <= haystack.length, needle.length <= 104`
• `haystack` and `needle` consist of only lowercase English characters.

### Implement strStr() LeetCode Solution in Java

``````public int strStr(String haystack, String needle) {
for (int i = 0; ; i++) {
for (int j = 0; ; j++) {
if (j == needle.length()) return i;
if (i + j == haystack.length()) return -1;
if (needle.charAt(j) != haystack.charAt(i + j)) break;
}
}
}
``````

### Implement strStr() LeetCode Solution in C++

``````class Solution {
public:
int strStr(string haystack, string needle) {
int m = haystack.size(), n = needle.size();
for (int i = 0; i <= m - n; i++) {
int j = 0;
for (; j < n; j++) {
if (haystack[i + j] != needle[j]) {
break;
}
}
if (j == n) {
return i;
}
}
return -1;
}
};
``````

### Implement strStr() LeetCode Solution in Python

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