poj 3450 Corporate Identity

题目链接：http://poj.org/problem?id=3450

题目分类：后缀数组

题意：求n个串的最长公共字串（输出字串）

//#include<bits/stdc++.h>
#include<stdio.h>
#include<math.h>
#include<algorithm>
#include<string.h>

using namespace std;

#define N 200005

int wa[N],wb[N],wsf[N],wv[N],sa[N];
int rank[N],height[N],s[N];
//sa:字典序中排第i位的起始位置在str中第sa[i]
//rank:就是str第i个位置的后缀是在字典序排第几
//height：字典序排i和i-1的后缀的最长公共前缀
int cmp(int *r,int a,int b,int k)
{
    return r[a]==r[b]&&r[a+k]==r[b+k];
}
void getsa(int *r,int *sa,int n,int m)//n要包含末尾添加的0
{
    int i,j,p,*x=wa,*y=wb,*t;
    for(i=0; i<m; i++)  wsf[i]=0;
    for(i=0; i<n; i++)  wsf[x[i]=r[i]]++;
    for(i=1; i<m; i++)  wsf[i]+=wsf[i-1];
    for(i=n-1; i>=0; i--)  sa[--wsf[x[i]]]=i;
    p=1;
    j=1;
    for(; p<n; j*=2,m=p)
    {
        for(p=0,i=n-j; i<n; i++)  y[p++]=i;
        for(i=0; i<n; i++)  if(sa[i]>=j)  y[p++]=sa[i]-j;
        for(i=0; i<n; i++)  wv[i]=x[y[i]];
        for(i=0; i<m; i++)  wsf[i]=0;
        for(i=0; i<n; i++)  wsf[wv[i]]++;
        for(i=1; i<m; i++)  wsf[i]+=wsf[i-1];
        for(i=n-1; i>=0; i--)  sa[--wsf[wv[i]]]=y[i];
        t=x;
        x=y;
        y=t;
        x[sa[0]]=0;
        for(p=1,i=1; i<n; i++)
            x[sa[i]]=cmp(y,sa[i-1],sa[i],j)? p-1:p++;
    }
}
void getheight(int *r,int n)//n不保存最后的0
{
    int i,j,k=0;
    for(i=1; i<=n; i++)  rank[sa[i]]=i;
    for(i=0; i<n; i++)
    {
        if(k)
            k--;
        else
            k=0;
        j=sa[rank[i]-1];
        while(r[i+k]==r[j+k])
            k++;
        height[rank[i]]=k;
    }
}

char str[N],ans[N];
int id[N],vis[4005];

bool check(int mid,int n,int k)
{
    int i,j,cnt = 0;
    memset(vis,0,sizeof(vis));
    for(i = 2; i<=n; i++)
    {
        if(height[i]<mid)
        {
            memset(vis,0,sizeof(vis));
            cnt = 0;
            continue;
        }
        if(!vis[id[sa[i-1]]])
        {
            cnt++;
            vis[id[sa[i-1]]] = 1;
        }
        if(!vis[id[sa[i]]])
        {
            cnt++;
            vis[id[sa[i]]] = 1;
        }
        if(cnt == k)
        {
            for(j = 0; j<mid; j++)
                ans[j] = s[sa[i]+j];
            ans[mid] = '';
            return 1;
        }
    }
    return 0;
}

int main()
{
    int n,i,j,k,len;
    while(~scanf("%d",&k),k)
    {
        n = 0;
        for(i = 0; i<k; i++)
        {
            scanf("%s",str);
            len = strlen(str);
            for(j = 0; j<len; j++)
            {
                s[n] = str[j];
                id[n] = i;
                n++;
            }
            s[n] = '#'+i;
            id[n] = '#'+i;
            n++;
        }
        s[n] = 0;
        getsa(s,sa,n+1,5000);
        getheight(s,n);
        int l = 1,r = len,mid,flag = 0;
        while(l<=r)
        {
            mid = (l+r)/2;
            if(check(mid,n,k))
            {
                flag = 1;
                l=mid+1;
            }
            else
                r=mid-1;
        }
        if(flag)
            printf("%s
",ans);
        else
            printf("IDENTITY LOST
");
    }

    return 0;
}