28. Implement strStr()

Posted 2020-08-30 CodesKiller

Implement strStr().

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

 此题的想法是遍历一遍haystack数组，当遍历到cur的元素和needle第一个char一样的时候，看haystack的子字符串是否和needle，代码如下：

 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 }

 本题也可以使用kmp的做法来做，希望第三遍刷的时候能掌握。