28. Implement strStr()

 1 public class Solution {
 2     public int strStr(String haystack, String needle) {
 3         int len = haystack.length();
 4         int index = -1;
 5         if(needle.length()==0) return 0;
 6         if(haystack.length()==0) return index;
 7         for(int i=0;i<len;i++){
 8             if(haystack.charAt(i)==needle.charAt(0)){
 9                 if(ismatch(haystack,needle,i)){
10                     index = i;
11                     break;
12                 }
13             }
14         }
15         return index;
16     }
17     public boolean ismatch(String haystack,String needle,int i){
18         int k = 0;
19         while(k<needle.length()&&(k+i)<haystack.length()&&haystack.charAt(i+k)==needle.charAt(k)){
20             k++;
21         }
22         if(k==needle.length()) return true;
23         return false;
24     }
25 }