BZOJ4755 [JSOI2016]扭动的回文串 【后缀数组】【manacher】

题目分析：

我写了史上最丑的后缀数组，怎么办？

首先manacher一遍两个串，这样只用考虑第三问。用$作为间隔符拼接两个串，把第一个串翻转。枚举回文中心，取最长的回文串，对于剩下的部分利用LCP匹配即可。

代码：

 #include<bits/stdc++.h>
 using namespace std;

 #define Sec first.second
 #define Fir first.first

 const int maxn = ;

 int n,as,f[maxn],sa[maxn],height[maxn],h[maxn],rk[maxn*];
 string s1,s2,vk;
 int RMQ[maxn][];

 void read(){cin >> n; cin >> s1 >> s2;}
 int pf[maxn][];

 void manacher(string &str){
     vk.clear();
     memset(f,,sizeof(f));
     for(int i=;i<n;i++) vk.push_back(str[i]),vk.push_back('$');
     f[] = ; int last = ,ct = ;
     for(int i=;i<*n;i++){
     f[i] = ;
     if(i <= ct+last- && i+f[*ct-i]- <= ct+last-) f[i]=f[*ct-i];
     while(i-f[i]>=&&i+f[i]<*n&&vk[i-f[i]]==vk[i+f[i]]){f[i]++;}
     if(ct+last- < i+f[i]-) ct = i,last = f[i];
     }
 }
 int X[maxn];
 pair<pair<int,int>,int> pr[maxn];
 vector <pair<int,int> > vec[maxn];
 void get_sa(){
     int z = s1.length();
     for(int i=;i<z;i++) X[s1[i]]++;
     for(int i=;i<=;i++)X[i] += X[i-];
     for(int i=;i<z;i++) rk[i] = X[s1[i]];
     for(int k=;(<<k)<=z;k++){
     for(int i=;i<z;i++)
         vec[rk[i+(<<k-)]].push_back(make_pair(rk[i],i));
     //pr[i+1]=make_pair(make_pair(rk[i],rk[i+(1<<k-1)]),i);
     //sort(pr+1,pr+z+1);
     for(int i=,tms=;i<=z;i++)
         for(int j=vec[i].size()-;j>=;j--){
         pr[++tms]=make_pair(make_pair(vec[i][j].first,i),vec[i][j].second);
         vec[i].pop_back();
         }
     for(int i=z;i>=;i--)
         vec[pr[i].Fir].push_back(make_pair(pr[i].Sec,pr[i].second));
     for(int i=,tms=;i<=z;i++)
         for(int j=vec[i].size()-;j>=;j--){
         pr[++tms] = make_pair(make_pair(i,vec[i][j].first),vec[i][j].second);
         vec[i].pop_back();
         }
     int num = ;
     for(int i=;i<=z;i++){
         if(pr[i].first == pr[i-].first) rk[pr[i].second]=num;
         else num++,rk[pr[i].second] = num;
     }
     }
     for(int i=;i<z;i++) sa[rk[i]] = i;
 }
 void get_height(){
     int z = s1.length();
     for(int i=;i<z;i++){
     if(i) h[i] = max(,h[i-]-); else h[i] = ;
     if(rk[i]==) continue;
     comp = sa[rk[i]-];
     while(s1[comp+h[i]] == s1[i+h[i]])h[i]++;
     }
     for(int i=;i<z;i++) height[rk[i]] = h[i];
     for(int i=;i<=z;i++) RMQ[i][] = height[i];
     for(int k=;(<<k)<=z;k++){
     for(int i=;i<=z;i++){
         if(i+(<<k-)>z) RMQ[i][k] = RMQ[i][k-];
         else RMQ[i][k] = min(RMQ[i][k-],RMQ[i+(<<k-)][k-]);
     }
     }
 }
 int getLCP(int L,int R){
     if(L == R) return n-sa[L]; if(L > R) swap(L,R); L++;
     int k = ; while((<<k+)<=R-L+)k++;
     return min(RMQ[L][k],RMQ[R-(<<k)+][k]);
 }

 void work(){
     manacher(s1);
     for(int i=;i<*n;i++) pf[i][] = f[i];
     manacher(s2);
     for(int i=;i<*n;i++) pf[i][] = f[i];
     for(int i=;i<n/;i++) swap(s1[i],s1[s1.length()-i-]);
     s1.push_back('$');
     for(int i=;i<n;i++) s1.push_back(s2[i]);
     get_sa(); get_height();
     for(int i=;i<*n;i+=) {
     if(pf[i][]%==)pf[i][]--;
     int z = (i-pf[i][]+)/,w = (i+pf[i][]-)/;
     int L = rk[n-z],R = rk[n+w+];
     if(L > R) swap(L,R); int len = getLCP(L,R); as=max(as,w-z++len*);
     if(pf[i][]%==)pf[i][]--;
     z = (i-pf[i][]+)/,w = (i+pf[i][]-)/;
     L = rk[n-z-],R = rk[n+w+];
     if(L > R) swap(L,R); len = getLCP(L,R); as = max(as,w-z++len*);
     }
     for(int i=;i<*n;i+=) {
     if(pf[i][]&) pf[i][]--;
     int z = i-pf[i][]+,w = i+pf[i][]-;
     if(pf[i][] == ){
         int L = rk[n-(i-)/-],R = rk[n++(i-)/];
         if(L > R) swap(L,R);int len=getLCP(L,R);as=max(as,len*);
     } else{
         z/=,w/=; int L = rk[n-z],R = rk[n++w];
         if(L > R) swap(L,R);int len=getLCP(L,R);as=max(as,w-z++len*);
     }
     if(pf[i][]&) pf[i][]--;
     z = i-pf[i][]+,w = i+pf[i][]-;
     if(pf[i][] == ){
         int L = rk[n-(i-)/-],R = rk[n++(i-)/];
         if(L>R) swap(L,R); int len = getLCP(L,R); as = max(as,len*);
     }else{
         z/=,w/=; int L = rk[n-z-],R = rk[n+w+];
         if(L > R) swap(L,R);int len=getLCP(L,R);as=max(as,w-z++len*);

     }
     }
     printf("%d",as);
 }

 int main(){
     //freopen("2.in","r",stdin);
     read();
     work();
     return ;
 }