# \[LeetCode] 28. Implement strStr()

Implement [strStr()](http://www.cplusplus.com/reference/cstring/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()](http://www.cplusplus.com/reference/cstring/strstr/) and Java's [indexOf()](https://docs.oracle.com/javase/7/docs/api/java/lang/String.html#indexOf\(java.lang.String\)).

**Analyse:**

​

**Solution:**

```swift
class Solution {
    
    func strStr(_ haystack: String, _ needle: String) -> Int {       
        if(needle.count == 0 ) {
            return 0;
        }
        
        if(haystack.count == 0) {
             return -1;
        }
        
        if(needle.count > haystack.count) {
            return -1;
        }
        
        let chars = Array(haystack);
        let needleChars = Array(needle);
        
        for i in 0..<chars.count - needleChars.count + 1 {
            let char = chars[i];
            
            var iNeedle = false;
            
            if(char == needleChars[0]) {
                iNeedle = true;
                
                for j in 1..<needleChars.count {
                    if(chars[j + i] != needleChars[j]) {
                         iNeedle = false;
                    }
                }
            }
            
            if(iNeedle == true) {
            
                return i;
            }
        }
        
        return -1;
    } 
}
```

**Solution 2:**

```swift
class Solution {
    func strStr(_ haystack: String, _ needle: String) -> Int {
        var output = -1
        var chars = Array(haystack)
        var needleChars = Array(needle)
        
        if(chars.count == 0) {
            if(needleChars.count != 0) {
                return -1
            } else {
                return 0
            }
            
        } else if(chars.count == 0 || needleChars.count == 0) {
            return 0
        } else if(needleChars.count > chars.count)  {
            return -1
        }

        for i in 0..<chars.count {
             
            let char = chars[i]
            
            if(char == needleChars[0]) {
                var isMatch = true
                var j = 1
                
                while (j < needleChars.count) {
                    
                    if(i + j >= chars.count) {
                        return -1
                    }
                    
                    let charA = chars[i + j]
                    let charB = needleChars[j]
                    
                    if(charA != charB) {
                        isMatch = false
                        break
                    }
                    
                    j += 1
                }
            
                if(isMatch == true) {
                    return i
                }
             
            }
            
        }
        
        return -1
        
    }
}
```