LeetCode 125 Implement strStr()

Implement strStr().

Returns a pointer to the first occurrence of needle in haystack, or null if needle is not part of haystack.

分析：

从0开始每次截取needle长度的字串来匹配，如果相等则找到。

public class Solution {
    public String strStr(String haystack, String needle) {
        
        int len = needle.length();
        for(int i=0; i<=haystack.length()-len; i++){
            String sub = haystack.substring(i,i+len);
            if(sub.equals(needle)){
                return haystack.substring(i);
            }
        }
        return null;
    }
}