妙用next數組打表求最小迴圈節len

標籤：迴圈   pow   a*   res   name   for   char   ==   printf   

#include <cstdio>#include <cstring>#include <iostream>#include <algorithm>using namespace std;int len;int n = 1000;int next[10000];int f[50000];char s[50000];int Pow(int a, int b){    int res=1;    while(b)    {        if(b&1)            res=res*a%7;        a=a*a%7;        b>>=1;    }    return res;}void getnext(){    int j=0,k=-1;    next[0]=-1;    while(j<n)    {        if(k==-1||s[j]==s[k])        {            next[++j]=++k;        }        else        {            k=next[k];        }    }}int main(){    for(int i=1;i<=600;i++)    {        f[i] = f[i-1] + Pow(i,i);        f[i]%=7;    }    for(int i=0;i<=600;i++)    {        sprintf(&s[i],"%d",f[i]);    }    s[601]='\0';    cout<<s<<endl;    getnext();    for(int i=1;i<=600;i++)          //由題意可知，長度為1的字串不算    {        len=i-next[i];              //len代表最小迴圈節        if(i%len==0 && i/len>1)      //周期大於1才是迴圈串        {            cout<<"ans = "<<len<<endl;        }    }    printf("\n");}

妙用next數組打表求最小迴圈節len