hdu 1358 KMP的应用

网上好多说得不够清楚，不过真正理解了KMP的next数组的含义，一点就通了。非优化的next数组的含义是：next[i]=k表示模式串下标为i的字符的前k个字符与开头的前k个字符相等，那么从0到i-1的模式串必然是循环的,循环节为从0到next[i] - (2 * next[i] - i)，其中 2 * next[i] - i表示的是从后往前的部分与从前往后的部分相交的长度。

/*
 * hdu1358/linux.cpp
 * Created on: 2011-8-29
 * Author    : ben
 */
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <algorithm>
using namespace std;

#define MAXN 1000005
int N;
char str[MAXN];
int nextval[MAXN];

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

void get_nextval() {
    int i = 0, j = -1;
    int parlen = N;
    char *pattern = str;
    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];
        }
    }
}

void get_next() {
    int i = 0, j = -1;
    int parlen = N;
    char *pattern = str;
    nextval[0] = -1;
    while (i <= parlen) {
        if (j == -1 || pattern[i] == pattern[j]) {
            i++;
            j++;
            nextval[i] = j;
        } else {
            j = nextval[j];
        }
    }
}

void work() {
    int T = 0, tmp;
    while (scanf("%d", &N) == 1 && N > 0) {
        scanf("%s", str);
        get_next();
        printf("Test case #%d\n", ++T);
        for (int i = 2; i <= N; i++) {
            tmp = i - nextval[i];
            if (i % tmp == 0 && i / tmp > 1) {
                printf("%d %d\n", i, i / tmp);
            }
        }
        putchar('\n');
    }
}