One of the string pattern matching algorithms: Naïve pattern matching algorithm

The string being searched is called the main string, and the strings to be searched are called pattern strings. The basic idea of naive pattern matching algorithm:

Starts each character of the main string as a substring and matches the pattern string. Cycle through the main string, and each character starts with a small loop of the length of the pattern string until the match succeeds or all traversal is complete.

The code implementation is simple:

    intSTRSTR (Char*haystack,Char*needle) { for(inti =0; ; ++i) { for(intj =0; ; ++J) {if(!needle[j])returnIif(!haystack[i + j])return-1;if(Needle[j]! = Haystack[i + j]) Break; }        }    }

The time complexity analysis of the naïve pattern matching algorithm is as follows:

Case	Complexity of Time	Note
Best case	O (1)	The match was successful at first.
Worst case scenario	O ((n-m+1) *m)	Each unsuccessful match occurs at the last character of the pattern string.
Average situation	O (N+M)	According to the equal probability principle, the average is (n+m)/2-time lookup.

Note: where n is the main string length, M is the pattern string length.

One of the string pattern matching algorithms: Naïve pattern matching algorithm