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;
}