【leetcode】Implement strStr()

 1 class Solution {
 2 public:
 3     int strStr(char *haystack, char *needle) {
 4        
 5         int n1=strlen(haystack);
 6         int n2=strlen(needle);          
 7         int result=-1;
 8         bool flag;
 9         for(int i=0;i<n1-n2+1;i++)
10         {
11             flag=true;
12             for(int j=0;j<n2;j++)
13             {
14                 if(haystack[i+j]==needle[j])
15                 {
16                     continue;
17                 }
18                 else
19                 {
20                     flag=false;
21                     break;
22                 }
23             }
24            
25             if(flag==true)
26             {
27                 result=i;
28                 break;
29             }
30         }          
31         return result;
32     }
33 };

 1 class Solution {
 2 public:
 3     int strStr(char *haystack, char *needle) {         
 4        
 5         int i=0;
 6         int j=0;
 7         int n1=strlen(haystack);
 8         int n2=strlen(needle);
 9          
10         vector<int> next=getNext(needle);
11        
12         while(i<n1&&j<n2)
13         {
14             if(j==-1||haystack[i]==needle[j])
15             {
16                 i++;
17                 j++;
18             }
19             else
20             {
21                 j=next[j];
22             }
23         }
24        
25         if(j==n2)
26         {
27             return i-j;
28         }
29         else
30         {
31             return -1;
32         }
33     }
34    
35     vector<int> getNext(char *needle)
36     {
37         int n=strlen(needle);
38        
39         vector<int> next(n);
40         if(n==0)
41         {
42             return next;
43         }
44        
45         next[0]=-1;
46        
47         int i=0;
48         int k=-1;
49         while(i<n-1)
50         {
51             if(k==-1||needle[k]==needle[i])
52             {
53                 
54                 i++;
55                 k++;
56                 next[i]=k;
57             }
58             else
59             {               
60                 k=next[k];
61             }
62         }
63        
64         return next;
65        
66     }
67  
68 };