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 = 252000;
const int N = 100000;

int n,q;
char str[maxn];

int sa[maxn],rk[maxn],X[maxn],Y[maxn];
int height[maxn],h[maxn],RMQ[maxn][19];
int len[maxn],st1[maxn],st2[maxn];
long long stnum[maxn];

int chk(int x,int k){
    return rk[sa[x]]==rk[sa[x-1]]&&rk[sa[x]+(1<<k)]==rk[sa[x-1]+(1<<k)];
}

void getsa(){
    for(int i=0;i<n;i++) X[str[i]]++;
    for(int i=1;i<=N;i++) X[i] += X[i-1];
    for(int i=n-1;i>=0;i--) sa[X[str[i]]--] = i;
    for(int i = 2, num = 1;i <= n;i++)
    rk[sa[i]] = (str[sa[i]] == str[sa[i-1]]?num:++num);
    rk[sa[1]] = 1;
    for(int k=1;(1<<k-1)<=n;k++){
    for(int i=1;i<=N;i++) X[i] = 0;
    for(int i=n-(1<<k-1);i<n;i++) Y[i-n+(1<<k-1)+1]=i;
    for(int i=1,j=(1<<k-1)+1;i<=n;i++)
        if(sa[i]>=(1<<k-1))Y[j++]=sa[i]-(1<<k-1);
    for(int i=0;i<n;i++) X[rk[i]]++;
    for(int i=1;i<=N;i++) X[i]+=X[i-1];
    for(int i=n;i>=1;i--) sa[X[rk[Y[i]]]--] = Y[i];
    int num = 1; Y[sa[1]] = 1;
    for(int i=2;i<=n;i++) Y[sa[i]] = (chk(i,k-1)?num:++num);
    for(int i=0;i<n;i++) rk[i] = Y[i];
    if(num == n) break;
    }
}

void getheight(){
    for(int i=0;i<n;i++){
    if(i) h[i] = max(0,h[i-1]-1); else h[i] = 0;
    if(rk[i] == 1) continue;
    int comp = sa[rk[i]-1];
    while(str[comp+h[i]] == str[i+h[i]])h[i]++;
    }
    for(int i=0;i<n;i++) height[rk[i]] = h[i];
    for(int i=1;i<=n;i++) RMQ[i][0] = height[i];
    for(int k=1;(1<<k)<=n;k++){
    for(int i=1;i<=n;i++){
        if(i+(1<<k-1)>n) RMQ[i][k] = RMQ[i][k-1];
        else RMQ[i][k] = min(RMQ[i][k-1],RMQ[i+(1<<k-1)][k-1]);
    }
    }
}

int getLCP(int L,int R){
    if(L > R) swap(L,R);
    if(L == R) return n-sa[L];
    L++;
    int k = 0; while((1<<k+1)<=R-L+1)k++;
    return min(RMQ[L][k],RMQ[R-(1<<k)+1][k]);
}

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

long long ans[maxn];
void work(){
    getsa();
    getheight();
    for(int i=1;i<=n;i++) stnum[i] = stnum[i-1]+(n-sa[i])-height[i];
    for(int i=1;i<=q;i++){
    long long u,v; scanf("%lld%lld",&u,&v);
    if(u > v) swap(u,v); if(v > stnum[n]){ans[i] = -1;continue;}
    int pn = lower_bound(stnum+1,stnum+n+1,u)-stnum;
    int pm = lower_bound(stnum+1,stnum+n+1,v)-stnum;
    len[i] = min(height[pn]+u-stnum[pn-1],height[pm]+v-stnum[pm-1]);
    st1[i] = n-(sa[pn]+height[pn]+u-stnum[pn-1]);
    st2[i] = n-(sa[pm]+height[pm]+v-stnum[pm-1]);
    int LCP = getLCP(pn,pm); LCP = min(LCP,len[i]);
    ans[i]+=1ll*LCP*LCP;
    }
    for(int i=0;i<n/2;i++) swap(str[i],str[n-i-1]);
    memset(sa,0,sizeof(sa));
    memset(rk,0,sizeof(rk));
    memset(X,0,sizeof(X));
    memset(Y,0,sizeof(Y));
    memset(height,0,sizeof(height));
    memset(h,0,sizeof(h));
    memset(RMQ,0,sizeof(RMQ));
    getsa();
    getheight();
    for(int i=1;i<=q;i++){
    if(ans[i] == -1) continue;
    int LCP = getLCP(rk[st1[i]],rk[st2[i]]); LCP = min(LCP,len[i]);
    ans[i] += 1ll*LCP*LCP;
    }
    for(int i=1;i<=q;i++) printf("%lld
",ans[i]);
}

int main(){
    read();
    work();
    return 0;
}