BZOJ3230 相似子串 【后缀数组】

题目分析：

容易想到sa排好序之后，子串排名就是前面的子串减去height数组。所以正着做一遍，倒着做一遍就行了。

代码：

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

 const int maxn = ;
 const int N = ;

 int n,q;
 char str[maxn];

 int sa[maxn],rk[maxn],X[maxn],Y[maxn];
 int height[maxn],h[maxn],RMQ[maxn][];
 int len[maxn],st1[maxn],st2[maxn];
 long long stnum[maxn];

 int chk(int x,int k){
     return rk[sa[x]]==rk[sa[x-]]&&rk[sa[x]+(<<k)]==rk[sa[x-]+(<<k)];
 }

 void getsa(){
     for(int i=;i<n;i++) X[str[i]]++;
     for(int i=;i<=N;i++) X[i] += X[i-];
     for(int i=n-;i>=;i--) sa[X[str[i]]--] = i;
     for(int i = , num = ;i <= n;i++)
     rk[sa[i]] = (str[sa[i]] == str[sa[i-]]?num:++num);
     rk[sa[]] = ;
     for(int k=;(<<k-)<=n;k++){
     for(int i=;i<=N;i++) X[i] = ;
     for(int i=n-(<<k-);i<n;i++) Y[i-n+(<<k-)+]=i;
     for(int i=,j=(<<k-)+;i<=n;i++)
         if(sa[i]>=(<<k-))Y[j++]=sa[i]-(<<k-);
     for(int i=;i<n;i++) X[rk[i]]++;
     for(int i=;i<=N;i++) X[i]+=X[i-];
     for(int i=n;i>=;i--) sa[X[rk[Y[i]]]--] = Y[i];
     int num = ; Y[sa[]] = ;
     for(int i=;i<=n;i++) Y[sa[i]] = (chk(i,k-)?num:++num);
     for(int i=;i<n;i++) rk[i] = Y[i];
     if(num == n) break;
     }
 }

 void getheight(){
     for(int i=;i<n;i++){
     if(i) h[i] = max(,h[i-]-); else h[i] = ;
     if(rk[i] == ) continue;
     int comp = sa[rk[i]-];
     while(str[comp+h[i]] == str[i+h[i]])h[i]++;
     }
     for(int i=;i<n;i++) height[rk[i]] = h[i];
     for(int i=;i<=n;i++) RMQ[i][] = height[i];
     for(int k=;(<<k)<=n;k++){
     for(int i=;i<=n;i++){
         if(i+(<<k-)>n) 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) swap(L,R);
     if(L == R) return n-sa[L];
     L++;
     int k = ; while((<<k+)<=R-L+)k++;
     return min(RMQ[L][k],RMQ[R-(<<k)+][k]);
 }

 void read(){
     scanf("%d%d",&n,&q);
     scanf("%s",str);
 }

 long long ans[maxn];
 void work(){
     getsa();
     getheight();
     for(int i=;i<=n;i++) stnum[i] = stnum[i-]+(n-sa[i])-height[i];
     for(int i=;i<=q;i++){
     long long u,v; scanf("%lld%lld",&u,&v);
     if(u > v) swap(u,v); if(v > stnum[n]){ans[i] = -;continue;}
     int pn = lower_bound(stnum+,stnum+n+,u)-stnum;
     int pm = lower_bound(stnum+,stnum+n+,v)-stnum;
     len[i] = min(height[pn]+u-stnum[pn-],height[pm]+v-stnum[pm-]);
     st1[i] = n-(sa[pn]+height[pn]+u-stnum[pn-]);
     st2[i] = n-(sa[pm]+height[pm]+v-stnum[pm-]);
     int LCP = getLCP(pn,pm); LCP = min(LCP,len[i]);
     ans[i]+=1ll*LCP*LCP;
     }
     for(int i=;i<n/;i++) swap(str[i],str[n-i-]);
     memset(sa,,sizeof(sa));
     memset(rk,,sizeof(rk));
     memset(X,,sizeof(X));
     memset(Y,,sizeof(Y));
     memset(height,,sizeof(height));
     memset(h,,sizeof(h));
     memset(RMQ,,sizeof(RMQ));
     getsa();
     getheight();
     for(int i=;i<=q;i++){
     if(ans[i] == -) continue;
     int LCP = getLCP(rk[st1[i]],rk[st2[i]]); LCP = min(LCP,len[i]);
     ans[i] += 1ll*LCP*LCP;
     }
     for(int i=;i<=q;i++) printf("%lld\n",ans[i]);
 }

 int main(){
     read();
     work();
     return ;
 }