字串匹配的RabinKarp演算法的c語言實現
阿新 • • 發佈:2018-11-09
</pre><pre name="code" class="cpp">#include<string.h> int check( char *s1,char *s2,int n ); int main() { char s1[10000],s2[1000000]; int n,i,j,k; int T = 563; scanf( "%d",&n ); for( i = 0;i < n;++i ) { int key1 = 0,key2 = 0,temp = 1; int len1,len2; int count = 0; scanf( "%s %s",s1,s2 ); len1 = strlen(s1),len2 = strlen(s2); if( len1 > len2 ) { printf( "0\n" ); break; } for( j = 0;j < len1;++j ) { key1 = ( key1 * 26 + s1[j] - 'A' ) % T; key2 = ( key2 * 26 + s2[j] - 'A' ) % T; } for( j = 0;j < len1 - 1;++j ) temp = (temp % T * 26 % T) % T; // printf( "%d\n",temp ); // printf( "key1: %d key2 : %d\n",key1,key2 ); if( key1 == key2 && check(s1,s2,len1) ) ++count; for( j = 1;j <= len2 - len1;++j ) { int t = key2 - (s2[j-1] - 'A') * temp; if( t < 0 ) while( t < 0 ) t += T; key2 = ( t * 26 + s2[j+len1-1] - 'A' ) % T; // printf( "ignore: %c,add %c ",s2[j-1],s2[j+len1-1] ); // printf( "key2 : %d\n",key2 ); if( key2 != key1 ) continue; else { if( check( s1,s2 + j,len1 ) ) ++count; } } printf( "%d\n",count ); } return 0; } int check( char *a,char *b,int n ) { int i = 0; for( i = 0;i < n;++i ) if( a[i] != b[i] ) return 0; return 1; }
字串匹配的RabinKarp演算法就是將模式轉化為數字形式,然後在母版上尋找其數值與模式數值相同的片段,如果模式長度較長,則選用取模後所得數相同的值在進行精確驗證其是否相等。如果在文字搜尋中能夠匹配的次數很少,則其事件複雜度可以看做是O(n+m);下面程式是將字符集a-z看做是26位進位制的數值,然後對其進行求模尋找相等值,如果有在使用check函式精確驗證其正確性。