## Problem – Find the Index of the First Occurrence in a String LeetCode Solution

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`

.

**Example 1:**

**Input:** haystack = "sadbutsad", needle = "sad"
**Output:** 0
**Explanation:** "sad" occurs at index 0 and 6.
The first occurrence is at index 0, so we return 0.

**Example 2:**

**Input:** haystack = "leetcode", needle = "leeto"
**Output:** -1
**Explanation:** "leeto" did not occur in "leetcode", so we return -1.

**Constraints:**

`1 <= haystack.length, needle.length <= 10`^{4}

`haystack`

and `needle`

consist of only lowercase English characters.

## Find the Index of the First Occurrence in a String 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;
}
}
}
```

## Find the Index of the First Occurrence in a String 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;
}
};
```

## Find the Index of the First Occurrence in a String 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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