10. The algorithm is simple to achieve swift strstr () function.

Disclaimer: This article is a blogger original article, shall not be reproduced without the bloggers allowed. https://blog.csdn.net/huanglinxiao/article/details/91528192

Given a string and a needle haystack string, a position of the needle to find the first occurrence of the string (starting from 0) in the haystack string. If not, it returns -1.

Example 1:

Input: haystack = "hello", needle = "ll"
Output: 2
Example 2:

Input: haystack = "aaaaa", needle = "bba"
Output: -1

solution:

 func strStr(_ haystack: String, _ needle: String) -> Int {
        
        guard !needle.isEmpty else {
            return 0
        }
        guard needle.count <= haystack.count else {
            return -1
        }
        //1.拿到匹配的字符串needle
        //2.在特定的字符串haystack中遍历查找
        if haystack.contains(needle) {
            
            let hays: NSString =  haystack as NSString
            
            let index:Int  = hays.range(of: needle).location
            
            return index
            
        }else{
            return -1
        }
    }