POJ 1225 Substrings

http://poj.org/problem?id=1226

题意：给定n个串。求一个最长的串，使得这个串或者其反串在每个串中都出现过？

思路：先在大串里面加入正反串，然后二分，判定即可。

 #include<cstdio>
 #include<iostream>
 #include<cmath>
 #include<cstring>
 #include<algorithm>
 int num[],ws[],wv[],wb[],wa[];
 int n,m,rank[],sa[],h[],b[];
 int read(){
     int t=,f=;char ch=getchar();
     while (ch<''||ch>''){if (ch=='-')f=-;ch=getchar();}
     while (''<=ch&&ch<=''){t=t*+ch-'';ch=getchar();}
     return t*f;
 }
 bool cmp(int *r,int a,int b,int l){
     return r[a]==r[b]&&r[a+l]==r[b+l];
 }
 void da(int *r,int *sa,int n,int m){
     int *y=wb,*x=wa,*t,i,j,p;
     for (i=;i<m;i++) ws[i]=;
     for (i=;i<n;i++) x[i]=r[i];
     for (i=;i<n;i++) ws[x[i]]++;
     for (i=;i<m;i++) ws[i]+=ws[i-];
     for (i=n-;i>=;i--) sa[--ws[x[i]]]=i;
     for (p=,j=;p<n;m=p,j*=){
         for (p=,i=n-j;i<n;i++) y[p++]=i;
         for (i=;i<n;i++) if (sa[i]>=j) y[p++]=sa[i]-j;
         for (i=;i<m;i++) ws[i]=;
         for (i=;i<n;i++) wv[i]=x[y[i]];
         for (i=;i<n;i++) ws[wv[i]]++;
         for (i=;i<m;i++) ws[i]+=ws[i-];
         for (i=n-;i>=;i--) sa[--ws[wv[i]]]=y[i];
         for (t=x,x=y,y=t,i=,p=,x[sa[]]=;i<n;i++)
          x[sa[i]]=cmp(y,sa[i],sa[i-],j)?p-:p++;
     }
 }
 void cal(int *r,int n){
     int i,j,k=;
     for (i=;i<=n;i++) rank[sa[i]]=i;
     for (i=;i<n;h[rank[i++]]=k)
      for (k?k--:,j=sa[rank[i]-];r[i+k]==r[j+k];k++);
 }
 bool check(int x){
     int L,R;
     int hash[];
     for (int i=;i<=n;i++){
         L=i;
         while (L<=n&&h[L]<x) L++;
         if (L>n) break;
         R=L;
         while (R<=n&&h[R]>=x) R++;
         memset(hash,,sizeof hash);
         for (int j=L-;j<=R-;j++)
          if (b[sa[j]]<=m)
           hash[b[sa[j]]]=;
         int j=;
         for (j=;j<=m;j++)
          if (!hash[j]) break;
         if (j>m) return ;
         i=R;
     }
     return ;
 }
 void solve(){
     int l=,r=,ans;
     while (l<=r){
         int mid=(l+r)>>;
         if (check(mid)) ans=mid,l=mid+;
         else r=mid-;
     }
     printf("%d\n",ans);
 }
 int main(){
     int T=read();
     char s[];
     while (T--){
         m=read();n=;int sx=;
         for (int i=;i<=m;i++){
             scanf("%s",s);
             int len=strlen(s);
             for (int j=;j<len;j++)
              num[n]=s[j],b[n++]=i;
             num[n]=sx++;b[n++]=n+;
             for (int j=len-;j>=;j--)
              num[n]=s[j],b[n++]=i;
             num[n]=sx++;b[n++]=n+;
         }
         num[n]=;b[n]=n+;
         da(num,sa,n+,sx+);
         cal(num,n);
         solve();
     }
 }