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Language: Default Period
Description 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 Input The input consists of several test cases. Each test case consists of two lines. The first one contains N (2 <= N <= 1 000 000) – the size of the string S.The second line contains the string S. The input file ends with a line, having the number zero on it. Output For each test case, output "Test case #" and the consecutive test case number on a single line; then, for each prefix with length i that has a period K > 1, output the prefix size i and the period K separated by a single space; the prefix sizes must be in increasing Sample Input 3 aaa 12 aabaabaabaab 0 Sample Output Test case #1 2 2 3 3 Test case #2 2 2 6 2 9 3 12 4 Source |
题意：求长度为i（2<=i<=N）的前缀，若前缀是一个周期串，则输出长度i和它的最大周期；要找出所有满足条件的。
思路：next[i]数组里面存的是i位置前 字符串的相同前缀和后缀的最大长度，若它是一个周期串，那它必满足i%（i-next[i]）==0.
代码：
#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <string>
#include <map>
#include <stack>
#include <vector>
#include <set>
#include <queue>
#pragma comment (linker,"/STACK:102400000,102400000")
#define maxn 1005
#define MAXN 1000010
#define mod 1000000009
#define INF 0x3f3f3f3f
#define pi acos(-1.0)
#define eps 1e-6
typedef long long ll;
using namespace std;
int next[MAXN];
char str[MAXN];
int N;
void get_next()
{
int i=0,j=-1;
next[0]=-1;
while (i<N)
{
if (j==-1||str[i]==str[j])
{
i++;
j++;
next[i]=j;
}
else
j=next[j];
}
}
void KMP()
{
for (int i=1;i<=N;i++) //枚举所有长度，看它满不满足要求
{
if (!(i%(i-next[i]))&&(i/(i-next[i]))>1)//满足就输出
printf("%d %d\n",i,i/(i-next[i]));
}
}
int main()
{
int cas=1;
while (scanf("%d",&N)&&N)
{
scanf("%s",str);
get_next();
printf("Test case #%d\n",cas++);
KMP();
printf("\n");
}
return 0;
}
/*
3
aaa
12
aabaabaabaab
0
*/