Swift 实现strStr() - LeetCode

输入: haystack = "hello", needle = "ll"
输出: 2

输入: haystack = "aaaaa", needle = "bba"
输出: -1

func strStr(_ haystack: String, _ needle: String) -> Int {
    
    if needle.isEmpty {
        return 0
    }
    
    let array = haystack.components(separatedBy: needle)
    
    if array.first!.count == haystack.count {
        return -1
    }
    
    return array.first!.count
}

func strStr(_ haystack: String, _ needle: String) -> Int {
    
    if needle.isEmpty {
        return 0
    }
    let hLength = haystack.count
    let nLength = needle.count
    if hLength < nLength {
        return -1
    }
    
    let threshold = hLength - nLength
    
    for i in 0...threshold {
        if (haystack[haystack.index(haystack.startIndex, offsetBy: i)..<haystack.index(haystack.startIndex, offsetBy: i + nLength)] == needle) {
            return i
        }
    }
    
    return -1
}