#include<stdio.h>
#include<string.h>

typedef char Elemtype;

//生成前缀的长度
void GenPreFix( Elemtype *Pattern, int *PreFix )
{
	int LOLP = 0;			//length of largest prefix
	int NOCM;				//number of character matched
	int Patlen = strlen(Pattern);

	PreFix[0] = -1; 
	PreFix[1] = 0;

	for( NOCM=2; NOCM<Patlen+1; NOCM++ ) {
		while( LOLP>0 && Pattern[LOLP] != Pattern[NOCM-1] ) //cursor -1
			LOLP = PreFix[LOLP];
		if( Pattern[LOLP] == Pattern[NOCM-1] )// -1 
			LOLP++;
		PreFix[NOCM] = LOLP;
	}
}

//KMP匹配函数
void KmpStrMatching( Elemtype *Target, Elemtype *Pattern, int *prefix )
{
	int Patlen = strlen( Pattern );
	int Tarlen = 0;				//记录已查找的目标串长度
	int NextLength = 0;
	int flag = 0;				//标记是否匹配成功过

	while( '\0' != *Target  ) {
		for( int i=0; i<Patlen; i++ ) 
			if( *(Target+i) != *(Pattern+i) )
				break;

			if( i == Patlen ) {
				printf("位置%d处匹配成功!\n", Tarlen+1);
				flag = 1;
			}

			NextLength = i - prefix[i];  // i--已经匹配成功的字符数， i=0 --- prefix[0]=-1 表示没匹配到任何字符，向后移一位
			Target = Target + NextLength;
			Tarlen += NextLength;
	}

	if( 0 == flag )
		printf("匹配不成功!\n");
}


int main()
{
	Elemtype TargetStr[100], PatternStr[20];
	int prefix[21];		//下表从1到20有效
	printf("请输入目标字符串:\n");
	gets(TargetStr);

	printf("请输入模式字符串:\n");
	gets(PatternStr);

	GenPreFix( PatternStr, prefix );  // 检测通过
	
	KmpStrMatching( TargetStr, PatternStr, prefix );
	
	return 0;
}