kmp算法c++实现

kmp算法c++实现

// kmp.cpp : 定义控制台应用程序的入口点。
//

#include
#include
#include
using namespace std;

int main(int argc, char* argv[])
{
	string a;
	string b;
	cin >> a;
	cin >> b;
	int a_length = a.length();
	int b_length = b.length();
	vector next(b_length, 0);

	//求解next数组，跳转方式
	next[0] = -1;
	for (int i = 1; i < b_length; i++)
	{
		int j = i - 1;
		while (j >-1 && b[i] != b[next[j] + 1])
		{
			j = next[j];
			
		}
		if (j == -1 && b[0] != b[i])
			next[i] = -1;
		else
			next[i] = next[j] + 1;
	}
	

	//模式匹配
	int a_index = 0;
        int b_index = 0;

	
	while (a_index < a_length&&b_index < b_length)
	{
		if (b[b_index] == a[a_index] || (b[b_index] != a[a_index]&&b_index==0))
		{
			a_index++;
			b_index++;
		}
		else
		{
			b_index--; 
			while (b_index != -1&&b[b_index+1] != a[a_index])
			{
				b_index = next[b_index];
			}
			if (b_index == -1)
			{
				b_index = 0;
			}
			else
			{
				b_index++; 
			}
		}
		 
	}
	if (b_index == b_length)
		cout << a_index << endl;
	else
	{
		cout << "sorry" << endl;
		cout << b_index << endl;
	}

	
	return 0;
}