KMP算法非遞歸實現——菜鳥與高手的區別

#include <string>
using namespace std;

//來自網絡
//以計算下一個元素的next值爲中心
static void preKmp(const char *x, int len, int kmpNext[])
{
   int i, j;

   i = 0;
   j = kmpNext[0] = -1;
   while (i < len) 
   {
      while (j > -1 && x[i] != x[j])
         j = kmpNext[j];

      i++;
      j++;

      if (x[i] == x[j])
         kmpNext[i] = kmpNext[j];
      else
         kmpNext[i] = j;
   }
}

//原創
//以計算當前next值爲中心
//在while循環中修正next會錯過修正之間的序列
static void MyPreKmp( const char* x, int len, int kmpNext[] )
{
	kmpNext[0] = -1;
	int index = 1;

	while ( index < len )
	{
		//計算index處的next值
		int i = index-1;
		while ( true )
		{
			int j = kmpNext[ i ];

			if ( -1 == j || x[ j ] == x[ index-1 ] )
			{
				kmpNext[ index ] = j+1;
				break;
			}
			i = j;
		}
		index++;
	}

	for ( int i=1; i<len; i++ )
	{
		if ( x[i] == x[ kmpNext[i] ] )
			kmpNext[i] = kmpNext[ kmpNext[i] ];
	}
}

void main()
{
	string s ="abaabcac";
	int buffer[ 100 ];

	MyPreKmp( s.c_str(), s.size(), buffer ); 
	preKmp( s.c_str(), s.size(), buffer ); 
}