SPOJ - NSUBSTR Substrings(后缀自动机)
You are given a string S which consists of 250000 lowercase latin letters at most. We define F(x) as the maximal number of times that some string with length x appears in S. For example for string 'ababa' F(3) will be 2 because there is a string 'aba' that occurs twice. Your task is to output F(i) for every i so that 1<=i<=|S|.
Input
String S consists of at most 250000 lowercase latin letters.
Output
Output |S| lines. On the i-th line output F(i).
Example
Input:
ababa
Output:
3
2
2
1
1
F(x)表示S的所有长度为x的子串中,出现次数的最大值,题意为输出F(1),F(2).......F(n).
分析:
从根节点,到主轴上的每个一个节点的数量都赋为数量1,表示根节点到该节点形成的子串数量初始为1(非主轴上的节点是主轴上节点的状态分移出来的,所以初始的时候不赋值,通过后缀链接再赋值)
这样的话,一个节点的后缀链接的num就等于该节点的num+1,对于每个节点,都记录该节点长度出现的子串数量最大值即可
代码如下:
#include <iostream> #include <string.h> #include <algorithm> #include <stdio.h> using namespace std; const int N=250010; typedef long long ll; struct State { State *link,*go[26]; int step; int num; void clear() { num=0; link=0; step=0; memset(go,0,sizeof(go)); } }*root,*last; int cnt[N]; int lenA; State statePool[N*2],*b[N*2],*cur; void init() { cur=statePool; root=last=cur++; root->clear(); } void Insert(int w) { State *p=last; State *np=cur++; np->clear(); np->step=p->step+1; while(p&&!p->go[w]) p->go[w]=np,p=p->link; if(p==0) np->link=root; else { State *q=p->go[w]; if(p->step+1==q->step) np->link=q; else { State *nq=cur++; nq->clear(); memcpy(nq->go,q->go,sizeof(q->go)); nq->step=p->step+1; nq->link=q->link; q->link=nq; np->link=nq; while(p&&p->go[w]==q) p->go[w]=nq, p=p->link; } } last=np; } void tsort() { memset(cnt,0,sizeof(cnt)); State *p; for(p=statePool;p!=cur;p++) cnt[p->step]++; for(int i=1;i<=lenA;i++) cnt[i]+=cnt[i-1]; for(p=statePool;p!=cur;p++) b[--cnt[p->step]]=p; } char A[N],B[N]; int ans[N]; int main() { while(scanf("%s",A)!=EOF){ init(); lenA=strlen(A); for(int i=0;i<lenA;i++) Insert(A[i]-'a'); tsort(); memset(ans,0,sizeof(ans)); State *p; p=root; for(int i=0;i<lenA;i++) { int x=A[i]-'a'; p=p->go[x]; p->num=1; } int L=cur-statePool; for(int i=L-1;i>0;i--) { p=b[i]; ans[p->step]=max(ans[p->step],p->num); p->link->num+=p->num; } for(int i=lenA-1;i>=1;i--) ans[i]=max(ans[i],ans[i+1]); for(int i=1;i<=lenA;i++) { printf("%d\n",ans[i]); } } return 0; }