KMP算法

对于KMP算法，最重要的是要把握其中的next数组的含义及求法

考虑一个模式字符串：b1b2...bn，定义next[s]如下：

next[s]  is the longest proper prefix of b1b2...bs that is also a suffix of b1b2...bs

#include "kmp.h"

#include <string.h>

void makeNext(const char* patt, int* next){

	int len = strlen(patt);

	//next must be an array with len + 1 element

	next[1] = 0;

	int s = 0;

	const char *p = patt - 1;

	for (int t = 1; t < len; t++){

		while (s > 0 && p[t + 1] != p[s + 1])

			s = next[s];

		if (p[t + 1] == p[s + 1]){

			s += 1;

			next[t + 1] = s;

		}

		else

			next[t + 1] = 0;

	}

}

int search(const char* src, const char* patt){

	int pattLen = strlen(patt);

	int srcLen = strlen(src);

	int *next = new int[pattLen + 1];

	memset(next, 0, (pattLen + 1) * sizeof(int));

	makeNext(patt, next);

	int i = 0;

	int j = 0;

	int result = -1;

	for (i = 0; i < srcLen; i++){

		while (j > 0 && src[i] != patt[j])

			j = next[j];

		if (src[i] == patt[j])

			j++;

		if (j == pattLen){

			result = i - pattLen + 1;

			break;

		}

	}

	return result;

}