【poj2406】next数组求循环节

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题目分析

本题主要考察kmp中next数组在求循环时的运用：

• 字符串是循环的： len % (len - next[len]) == 0

• 字符串循环次数： len / (len - next[len])

• 字符串循环节长度： len - next[len]

code

#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<cmath>
#include<cstring>
#include<algorithm>
#include<ctime>
using namespace std;
const int N = 1000100;
char s[N];
int next[N], lS, ans;
inline void getNext(){
	for(int i = 2, j = 0; i <= lS; i++){
		while(j && s[i] != s[j + 1]) j = next[j];
		if(s[i] == s[j + 1]) j++;
		next[i] = j;
	}
}
int main(){
	while(~scanf("%s", s + 1), s[1] != '.'){
		memset(next, 0, sizeof next);
		lS = strlen(s + 1);
		getNext();
		if(lS % (lS - next[lS]) == 0)
			ans = lS / (lS - next[lS]);
		else ans = 1;
		cout<<ans<<endl;
	}
	return 0;
}