KMP算法（C++）

KMP 算法实现，记录一下，后面有时间再详细说明

#include<iostream>
#include<vector>
using namespace std;

vector<int> getNext(string p)
{
	vector<int> next(p.length(),0);
	next[0] = -1;
	int len = p.length();
	int k = -1; int j = 0;
	while (j<len-1)
	{
		if (k == -1 || p[k] == p[j])
		{
			k++;
			j++;
			next[j] = k;
		}
		else {
			k = next[k];
		}
	}
	return next;
}

int KMP(string s, string p)
{
	int i = 0; int j = 0;
	auto next = getNext(p);
	while (i < s.length() && j < p.length())
	{
		if (j==-1 || s[i]==p[j])
		{
			i++;
			j++;
		}
		else {
			j = next[j];
		}
	}
	if (j == p.length())
	{
		return i - j;
	}else
		return -1 ;
}

int main()

{
	string s = "ababcdeac";
	string p = "abc";
	cout << KMP(s, p) << endl;
	system("pause");
	return 0;
}