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`.

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
```

Example 3:

```Input: haystack = "", needle = ""
Output: 0
```

Constraints:

• `0 <= haystack.length, needle.length <= 5 * 104`
• `haystack` and `needle` consist of only lower-case English characters.

28. Implement strStr()
``````struct Solution;

impl Solution {
fn str_str(haystack: String, needle: String) -> i32 {
match haystack.find(&needle) {
Some(index) => index as i32,
None => -1,
}
}
}

#[test]
fn test() {
assert_eq!(Solution::str_str("hello".to_string(), "ll".to_string()), 2);
assert_eq!(
Solution::str_str("aaaaa".to_string(), "bba".to_string()),
-1
);
}
``````