【POJ 2406】 Power Strings

【题目链接】

点击打开链接

【算法】

KMP

如果字符串中存在循环节，则next[len] = (循环节个数 - 1） * 循环节长度

循环节个数 = len / (len - next[len])

【代码】

#include <algorithm>
#include <bitset>
#include <cctype>
#include <cerrno>
#include <clocale>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <limits>
#include <list>
#include <map>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <utility>
#include <vector>
#include <cwchar>
#include <cwctype>
#include <stack>
#include <limits.h>
using namespace std;
#define MAXL 10000010

int len;
char s[MAXL];
int next[MAXL];

template <typename T> inline void read(T &x) {
        int f = ; x = ;
        char c = getchar();
        for (; !isdigit(c); c = getchar()) { if (c == '-') f = -f; }
        for (; isdigit(c); c = getchar()) x = (x << ) + (x << ) + c - '';
        x *= f;
}
template <typename T> inline void write(T x) {
    if (x < ) { putchar('-'); x = -x; }
    if (x > ) write(x/);
    putchar(x%+'');
}
template <typename T> inline void writeln(T x) {
    write(x);
    puts("");
}

inline void getnext() {
        int i,pos;
        next[] = ;
        for (i = ; i <= len; i++) {
                pos = next[i-];
                while (pos >  && s[pos+] != s[i]) pos = next[pos];
                if (s[i] == s[pos+]) next[i] = pos + ;
                else next[i] = ;
        }
}

int main() {

        while (true) {
                scanf("%s",s+);
                if (s[] == '.') return ;
                len = strlen(s+);
                getnext();
                if (len % (len - next[len]) == ) writeln(len/(len-next[len]));
                else writeln();
        }

        return ;

}