hdu 1686 KMP

求模式串在主串中出现的次数，需要理解KMP后才能做，其实还是挺简单的，只要匹配完成一次后，j滑动到next[j]继续比较即可。刚开始一直TLE，上网找别人的代码比对，发现自己多写了一层循环，太粗心了……

/*
 * hdu1686/linux.cpp
 * Created on: 2011-8-29
 * Author    : ben
 */
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <algorithm>
using namespace std;

#define MAX_PAR_LEN 10005
#define MAX_TXT_LEN 1000005
char pattern[MAX_PAR_LEN], text[MAX_TXT_LEN];
int nextval[MAX_PAR_LEN], parlen, txtlen;

void get_nextval() {
    int i = 0, j = -1;
    nextval[0] = -1;
    while (i < parlen) {
        if (j < 0 || pattern[i] == pattern[j]) {
            i++;
            j++;
            if (pattern[i] != pattern[j]) {
                nextval[i] = j;
            } else {
                nextval[i] = nextval[j];
            }
        } else {
            j = nextval[j];
        }
    }
}

int kmp() {
    int i, j, ret = 0;
    get_nextval();
    j = i = 0;
    while (i < txtlen && j < parlen) {
        if (j == -1 || text[i] == pattern[j]) {
            i++;
            j++;
        } else {
            j = nextval[j];
        }
        if (j >= parlen) {
            ret++;
            j = nextval[j];//本题的关键代码
        }
    }
    return ret;
}

void work() {
    int T;
    scanf("%d", &T);
    while (T--) {
        scanf("%s%s", pattern, text);
        txtlen = strlen(text);
        parlen = strlen(pattern);
        printf("%d\n", kmp());
    }
}

int main() {
#ifndef ONLINE_JUDGE
    freopen("data.in", "r", stdin);
#endif
    work();
    return 0;
}