Implement strStr()

Problem:

Implement strStr().

Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

Analysis:

这道题在leetcode String分类里算简单的。是因为暴力法很简单易懂。更高级的有Rabin-Karp algorithm, KMP algorithm 和 Boyer0 Moore algorigthm。以上都是出现在高级算法设计课的。暂时达不到那个高度。

Solution:

1:  public static int strStr(String haystack, String needle)  
2:       {  
3:            int hlen=haystack.length();  
4:            int nlen=needle.length();  
5:            if(haystack==null || needle==null || nlen<hlen)  
6:                 return -1;  
7:            boolean isSub=true;  
8:            for(int i=0;i<hlen-nlen;i++)  
9:            {  
10:          isSub=true;          
11:             for(int j=0;j<nlen;j++)  
12:             {  
13:                  if(haystack.charAt(i+j)!=needle.charAt(j))  
14:               {  
15:                   isSub=false;  
16:                   break;  
17:               }  
18:             }  
19:             if(isSub)  
20:                 return i;   
21:            }  
22:            return -1;  
23:       }