UVA 11107（后缀数组）

(http://acm.hust.edu.cn/vjudge/contest/view.action?cid=105595#problem/A)
题意：给定n个字符串，求出最长子串，在超过n/2的串中出现过。
做法：后缀数组+尺取

#include <stdio.h>
#include <iostream>
#include <algorithm>
#include <string.h>
#include <vector>

using namespace std;

#define ll long long
#define inf 1e18
#define clr(x,y) memset(x,y,sizeof x)
#define FOR(i,a,b) \
    for(i=a;a<b?i<=b:i>=b;a<b?i++:i--)

const int maxn = 2e5+20;

char s[maxn];
int sa[maxn],t[maxn],t2[maxn],c[maxn],len;

void build_sa(int m)
{
    int n=len;
    int i,*x = t,*y = t2;

    FOR(i,0,m-1) c[i]=0;
    FOR(i,0,n-1) c[x[i]=s[i]]++;

    FOR(i,1,m-1) c[i]+=c[i-1];
    FOR(i,n-1,0) sa[--c[x[i]]]=i;

    for(int k=1;k<=n;k<<=1){
        int p=0;
        FOR(i,n-k,n-1) y[p++]=i;
        FOR(i,0,n-1) if(sa[i]>=k) y[p++]=sa[i]-k;

        FOR(i,0,m-1) c[i]=0;
        FOR(i,0,n-1) c[x[y[i]]]++;

        FOR(i,0,m-1) c[i]+=c[i-1];
        FOR(i,n-1,0) sa[--c[x[y[i]]]]=y[i];

        swap(x,y);
        p=1;
        x[sa[0]]=0;
        FOR(i,1,n-1)
            x[sa[i]]=y[sa[i-1]]==y[sa[i]] &&
            y[sa[i-1]+k]==y[sa[i]+k]?p-1:p++;
        if(p>=n) break;
        m=p;
    }
}

int Rank[maxn],height[maxn];
int id[maxn];

void getHeight()
{
    int k=0,n=len;
    for(int i=0;i<n;i++) Rank[sa[i]]=i;
    for(int i=0;i<n;i++)
    {
        if(k) k--;
        int j=sa[Rank[i]-1];
        while(s[i+k]==s[j+k] && s[i+k]!='$' )
            k++;
        height[Rank[i]]=k;
    }
}

int d[maxn][20] , flog[maxn];
void RMQ_init(int n)
{
    for(int i=0;i<n;i++) d[i][0] = height[i];
    flog[0]=-1;
    for(int i=1;i<n;i++) flog[i]=flog[i>>1]+1;
    for(int j=1;(1<<j)<=n;j++)
        for(int i=0;i+(1<<j)<=n;i++)
            d[i][j] = min(d[i][j-1],d[i+(1<<(j-1))][j-1]);
}

int RMQ(int L,int R)
{
    int k = flog[R-L+1];
    return min(d[L][k],d[R-(1<<k)+1][k]);
}

char ss[maxn];
int cnt[maxn],sum;

void add(int pos)
{
    if( s[sa[pos]] == '$' )
        return ;
    if( cnt[id[sa[pos]]] == 0 )
        sum++;
    cnt[id[sa[pos]]]++;
}

void del(int pos)
{
    if( s[sa[pos]] == '$' )
        return ;
    if( cnt[id[sa[pos]]] == 1 )
        sum--;
    cnt[id[sa[pos]]]--;
}

int main()
{
    //freopen("input.txt","r",stdin);
    //freopen("output.txt","w",stdout);
    //printf("%d\n",1<<20);
    int n;
    int fi=1;
    while(~scanf("%d",&n))
    {
        if( n == 0 ) break;
        if( fi ) fi=0;
        else printf("\n");
        if( n == 1 )
        {
            scanf("%s",ss);
            printf("%s\n",ss);
            continue;
        }
        len=0;
        for(int i=0;i<n;i++)
        {
            scanf("%s",ss);
            strcat(ss,"$");
            int l = strlen(ss);
            for(int j=0;j<l;j++)
            {
                s[len]=ss[j];
                id[len]=i;
                len++;
            }
        }
        s[len++]=0;
        build_sa(255);
        getHeight();
        RMQ_init(len);

//        for(int i=0;i<len;i++)
//          printf("%d %s id %d height %d\n",i,s+sa[i],id[sa[i]],height[i]);

        clr(cnt,0);
        sum=0;

        int he=1,st=0;
        int longlen = -1;
        vector<int>q;
//        printf("len %d\n",len);
        while( st < len )
        {
            while( st < len )
            {
                add(++st);
                if( sum*2>n )
                    break;
            }
            if( st == len )
                break;
            while( he < len )
            {
                del(he++);
                if( sum*2<=n )
                {
                    add(--he);
                    break;
                }
            }
//          printf("he %d st %d\n",he,st);
            int la = RMQ(he+1,st);
            if( la > longlen )
            {
                longlen = la;
                q.clear();
                q.push_back(he);
            }
            else if( la == longlen )
                q.push_back(he);
            del(he++);
        }
        if( q.size() && longlen > 0 )
        {
            for(int i=0;i<q.size();i++)
            {
                //printf("%d*\n",q[i]);
                if( i && RMQ(q[i-1]+1,q[i]) >= longlen  )
                    continue;
                for(int j=0;j<longlen;j++)
                    printf("%c",s[sa[q[i]]+j]);
                printf("\n");
            }
        }else
            printf("?\n");
    }
    return 0;
}