HDU-1358-Period(KMP, 循环节)

链接:

https://vjudge.net/problem/HDU-1358#author=0

题意:

For each prefix of a given string S with N characters (each character has an ASCII code between 97 and 126, inclusive), we want to know whether the prefix is a periodic string. That is, for each i (2 <= i <= N) we want to know the largest K > 1 (if there is one) such that the prefix of S with length i can be written as A K , that is A concatenated K times, for some string A. Of course, we also want to know the period K.

思路:

先求出Next数组, 然后遍历一遍, 求出每个前缀的循环节, 再判断是否满足即可.

代码:

#include <iostream>
#include <cstdio>
#include <cstring>
#include <vector>
//#include <memory.h>
#include <queue>
#include <set>
#include <map>
#include <algorithm>
#include <math.h>
#include <stack>
#include <string>
#include <assert.h>
#include <iomanip>
#include <iostream>
#include <sstream>
#define MINF 0x3f3f3f3f
using namespace std;
typedef long long LL;
const int MAXN = 1e6+10;

int Next[MAXN];
char s[MAXN], p[MAXN];

void GetNext()
{
    int len = strlen(p);
    Next[0] = -1;
    int j = 0;
    int k = -1;
    while (j < len)
    {
        if (k == -1 || p[k] == p[j])
        {
            ++k;
            ++j;
            Next[j] = k;
        }
        else
            k = Next[k];
    }
}

int main()
{
    int cnt = 0, n;
    while (~scanf("%d", &n) && n)
    {
        scanf("%s", p);
        GetNext();
        printf("Test case #%d\n", ++cnt);
        for (int i = 2;i <= n;i++)
        {
            int len = i-Next[i];
            if (len != i && i%len == 0)
                printf("%d %d\n", i, i/len);
        }
        puts("");
    }

    return 0;
}