[BZOJ1031][JSOI2007]字符加密Cipher（后缀数组）

题目描述

题解

代码

#include<iostream>
#include<cstring>
#include<cstdio>
using namespace std;
const int max_n=5e5+5;
int n,m=300;
char s[max_n];
int sa[max_n],c[max_n],x[max_n],y[max_n];
inline void build_sa(){
for (int i=0;i<m;++i) c[i]=0;
for (int i=0;i<n;++i) c[x[i]=s[i]]++;
for (int i=1;i<m;++i) c[i]+=c[i-1];
for (int i=n-1;i>=0;--i) sa[--c[x[i]]]=i;

for (int k=1;k<=n;k<<=1){
int p=0;
for (int i=n-k;i<n;++i) y[p++]=i;
for (int i=0;i<n;++i) if (sa[i]>=k) y[p++]=sa[i]-k;

for (int i=0;i<m;++i) c[i]=0;
for (int i=0;i<n;++i) c[x[y[i]]]++;
for (int i=1;i<m;++i) c[i]+=c[i-1];
for (int i=n-1;i>=0;--i) sa[--c[x[y[i]]]]=y[i];

swap(x,y);
p=1; x[sa[0]]=0;
for (int i=1;i<n;++i) x[sa[i]]=y[sa[i-1]]==y[sa[i]]&&
((sa[i-1]+k>=n?-1:y[sa[i-1]+k])==(sa[i]+k>=n?-1:y[sa[i]+k]))?p-1:p++;
if (p>n) break;
m=p;
}
}
int main(){
gets(s);
n=strlen(s);
for (int i=0;i<n;++i) s[n+i]=s[i];
n*=2;
build_sa();
for (int i=0;i<n;++i)
if (sa[i]<n/2)
putchar(s[sa[i]+n/2-1]);
putchar('\n');
}

总结