Implement strStr () Leetcode Java

Describe
Implement strStr ().
Returns A pointer to the first occurrence of needle in haystack, or null if needle are not part of haystack.
Analysis
The complexity of the brute force algorithm is O (M n), as shown in the code below. More efficient algorithms have KMP algorithms, boyer-mooer algorithms, and
Rabin-karp algorithm. There are plenty of brute force algorithms in the interview, so be sure to write them without bugs.

Needle is not a substring of haystack, yes then return this substring

Code

1  Public classStrinstr {2 3      Public Static voidMain (string[] args) {4         //TODO auto-generated Method Stub5String haystack = "1strstr12str";6String needle= "str"; 7 System.out.println (strStr (haystack, needle));8 9     }Ten      Public Staticstring StrStr (string str,string s) { One         if(str== "") { A             returnstr; -         } -         CharKey=s.charat (0); the         intIndex=0; - //int Index=str.indexof (key); -         Char[] Sch=S.tochararray (); -         Char[] Strch=Str.tochararray (); +  -          while(Index!=-1) { +index=Str.indexof (key); A              for(inti=0;i<sch.length;i++) { at                 if(sch[i]==strch[index+i]) { -                     returns; -                 } -             } -Str=str.substring (index+1); -              in         } -         return NULL; to     } +     




 -      the      * //Method Two $      Public Staticstring StrStr2 (String haystack, string needle) {Panax Notoginseng              if(needle.length () = = 0) -                 returnhaystack; the             +               for(inti = 0; I < haystack.length (); i++) { A                   if(Haystack.length ()-i + 1 <needle.length ()) the                       return NULL; +             -                   intK =i; $                  intj = 0; $            -                   while(J < Needle.length () && K < Haystack.length () && Needle.charat (j) = =Haystack.charat (k)) { -J + +; thek++; -                      if(J = =needle.length ())Wuyi                          returnhaystack.substring (i,k); the                  } -            Wu              } -              return NULL; About          } $}

Implement strStr () Leetcode Java