POJ1961 Period && POJ2604 Power Strings 字符串循环节

两道题都是求循环节的。。。但是一道是学哈希时做的，另一道是学$KMP$时做的

---

POJ2604 用的哈希。。。枚举长度的因数作为循环节的长度，然后暴力算出所有循环节位置的哈希值，看看是否相等。

#include<cstdio>
#include<iostream>
#include<algorithm>
#include<cstring>
#include<cmath>
#include<cctype>
#include<cstdlib>
#include<vector>
#include<queue>
#include<map>
#include<set>
#define ll unsigned long long
#define R register int
using namespace std;
namespace Fread {
    static char B[1<<15],*S=B,*D=B;
    #define getchar() (S==D&&(D=(S=B)+fread(B,1,1<<15,stdin),S==D)?EOF:*S++)
    inline int g() {
        R ret=0,fix=1; register char ch; while(!isdigit(ch=getchar())) fix=ch=='-'?-1:fix;
        do ret=ret*10+(ch^48); while(isdigit(ch=getchar())); return ret*fix;
    }
}using Fread::g;
const int B=131,N=1000010;
ll f[N],p[N];
inline ll calc(int l,int r) {return f[r]-f[l-1]*p[r-l+1];}
signed main() {
#ifdef JACK
    freopen("NOIPAK++.in","r",stdin);
#endif
    p[0]=1; for(R i=1;i<=N-10;++i) p[i]=p[i-1]*B;
    while(1) { register char s[N]; 
        scanf("%s",s+1); R n=strlen(s+1); 
        if(n==1&&s[1]=='.') break;
        for(R i=1;i<=n;++i) f[i]=f[i-1]*B+s[i]-96;
        for(R i=1;i<=n;++i) if(n%i==0) { register ll tmp=calc(1,i); 
            register bool flg=false; 
            for(R l=i+1;l<=n;l+=i) { 
                if(tmp!=calc(l,l+i-1)) {flg=1; break;}
            } if(!flg) {printf("%d
",n/i);break;}
        } 
    }
}

---

POJ1961 用的$kmp$详解

#include<cstdio>
#include<iostream>
#include<algorithm>
#include<cstring>
#include<cmath>
#include<cctype>
#include<cstdlib>
#include<vector>
#include<queue>
#include<map>
#include<set>
#define ull unsigned long long
#define ll long long
#define R register int
using namespace std;
namespace Fread {
    static char B[1<<15],*S=B,*D=B;
    #define getchar() (S==D&&(D=(S=B)+fread(B,1,1<<15,stdin),S==D)?EOF:*S++)
    inline int g() {
        R ret=0,fix=1; register char ch; while(!isdigit(ch=getchar())) fix=ch=='-'?-1:fix;
        do ret=ret*10+(ch^48); while(isdigit(ch=getchar())); return ret*fix;
    } inline bool isempty(const char& ch) {return ch<=36||ch>=127;}
    inline void gs(char* s) {register char ch; while(isempty(ch=getchar())); do *s++=ch; while(!isempty(ch=getchar()));}
}using Fread::g; using Fread::gs;
const int N=1000010;
char s[N]; int nxt[N],n,t;
inline void PRE() { nxt[1]=0;
    for(R i=2,j=0;i<=n;++i) {
        while(j&&s[i]!=s[j+1]) j=nxt[j];
        if(s[i]==s[j+1]) ++j; nxt[i]=j;
    }
}
signed main() {
#ifdef JACK
    freopen("NOIPAK++.in","r",stdin);
#endif
    while(n=g(),n>0) {
        gs(s+1); PRE(); printf("Test case #%d
",++t);
        for(R i=2;i<=n;++i) {
            if(i%(i-nxt[i])==0&&i/(i-nxt[i])>1)
                printf("%d %d
",i,i/(i-nxt[i]));
        } printf("
");
    }
}

---

2019.06.27