KMP Pattern-Matching

2017/kmp.cpp

+#include <cstdio>
+#include <algorithm>
+#include <cstring>
+
+#define MAXN 1000010
+
+using namespace std;
+
+int P[ MAXN + 1 ];
+
+void prefix( char pattern[] )
+{
+	int N = strlen( pattern );
+	P[ 0 ] = -1;
+	for( int i = 1; i < N; i++ ) {
+		int j = P[ i - 1 ];
+		while( true ) {
+			if( pattern[ i ] == pattern[ j + 1 ] ) {
+				P[ i ] = j + 1;
+				break;
+			}
+			else if( j == -1 ) {
+				P[ i ] = -1;
+				break;
+			} else {
+				j = P[ j ];
+			}
+		}
+	}
+}
+
+
+
+
+
+int KMP( char text[], char pattern[] )
+{
+	int i = 0, j = 0, N = strlen( text ), M = strlen( pattern );
+	prefix( pattern );
+	while( true ) {
+		if( i == N ) {
+			break;
+		}
+		if( text[ i ] == pattern[ j ] ) {
+			if( j == M - 1 ) {
+				return i - M;
+			}
+			i++;
+			j++;
+		}
+		else if( j == 0 ) {
+			i++;
+		} else {
+			j = P[ j ];
+		}
+	}
+	return 0;
+}
+
+int main( void )
+{
+	char text[ MAXN + 1 ], pattern[ MAXN + 1 ];
+	scanf("%s%s", text, pattern );
+	int res = KMP( text, pattern );
+	if( res ) {
+		printf("%s occurs in %s with shift %d\n", pattern, text, res + 1 );
+	} else {
+		printf("%s does not occur in %s\n", pattern, text );
+	}
+	return 0;
+}