【分析】
参见论文
//poj 3693 Maximum repetition substring #include<cstdio> #include<cstring> #include<iostream> #include<algorithm> #define ll long long #define M(a) memset(a,0,sizeof a) #define fo(i,j,k) for(i=j;i<=k;i++) using namespace std; const int mxn=200005; int n,m,T,len,ans,lef,rig; char s[mxn]; int st[mxn][30],rank[mxn],height[mxn]; int a[mxn],b[mxn],x[mxn],y[mxn],sa[mxn]; inline bool comp(int i,int j,int l) { return y[i]==y[j]&&(i+l>len?-1:y[i+l])==(j+l>len?-1:y[j+l]); } inline void work() { int i,j,k,p;m=200; fo(i,0,m) b[i]=0; fo(i,1,len) b[x[i]=a[i]]++; fo(i,1,m) b[i]+=b[i-1]; for(i=len;i>=1;i--) sa[b[x[i]]--]=i; for(k=1;k<=len;k<<=1) { p=0; fo(i,len-k+1,len) y[++p]=i; fo(i,1,len) if(sa[i]>k) y[++p]=sa[i]-k; fo(i,0,m) b[i]=0; fo(i,1,len) b[x[y[i]]]++; fo(i,1,m) b[i]+=b[i-1]; for(i=len;i>=1;i--) sa[b[x[y[i]]]--]=y[i]; swap(x,y),p=2,x[sa[1]]=1; fo(i,2,len) x[sa[i]]=comp(sa[i-1],sa[i],k)?p-1:p++; if(p>len) break; m=p; } p=k=0; fo(i,1,len) rank[sa[i]]=i; for(i=1;i<=len;height[rank[i++]]=k) for(k?k--:0,j=sa[rank[i]-1];a[i+k]==a[j+k];k++); } inline void init() { int i,j; fo(i,1,len) st[i][0]=height[i]; fo(j,1,28) fo(i,1,len) if((i+(1<<j)-1)<=len) st[i][j]=min(st[i][j-1],st[i+(1<<j-1)][j-1]); } inline int query(int x,int y) { if(x>y) swap(x,y); x++; int k=0; while(x+(1<<k+1)<=y) k++; return min(st[x][k],st[y-(1<<k)+1][k]); } int main() { int i,j,l,r,L; while(1) { M(a); ans=lef=rig=0; scanf("%s",s+1); len=strlen(s+1); fo(i,1,len) a[i]=s[i]; if(len==1 && s[1]=='#') break; printf("Case %d: ",++T); work(),init(); fo(L,1,len/2) { for(i=1;i*L+1<=len;i++) { int x=(i-1)*L+1,y=i*L+1; if(s[x]!=s[y]) continue; r=y+query(rank[x],rank[y])-1; fo(j,0,L-1) { if(x-j<1 || s[x-j]!=s[y-j]) break; int tmp=(r-(x-j)+1)/L; if(tmp>ans || (tmp==ans && rank[x-j]<rank[lef])) lef=x-j,rig=lef+tmp*L-1,ans=tmp; } } } if(ans==0) printf("%c",s[sa[1]]); else fo(i,lef,rig) printf("%c",s[i]); printf("\n"); } return 0; } /* xbcabcab */
