1 package leetcode;
 2 
 3 public class demo_28 {
 4     public int strStr(String haystack, String needle) {
 5         int i;
 6         if(needle=="") {return 0;}
 7         if(haystack.contains(needle)) {
 8             for(i=0;i<haystack.length();i++) {
 9                 if(haystack.substring(i,i+needle.length()).equals(needle)) {
10                     break;
11                 }
12             }
13             return i;
14         }
15         else {
16             return -1;
17         }
18     }
19     public static void main(String[] args) {
20         // TODO Auto-generated method stub
21         demo_28 d28 = new demo_28();
22         String haystack="hello";
23         String needle="ll";
24         System.out.println(d28.strStr(haystack, needle));
25     }
26 
27 }

简化版

1 return haystack.indexOf(needle);

 KMP算法