ural 1517. Freedom of Choice (后缀数组，最长公共子串)

  1/* ***********************************************
  2Author :111qqz
  3Created Time :2016年07月31日 星期日 00时36分19秒
  4File Name :code/ural/1517.cpp
  5************************************************ */
  6#include <cstdio>
  7#include <cstring>
  8#include <iostream>
  9#include <algorithm>
 10#include <vector>
 11#include <queue>
 12#include <set>
 13#include <map>
 14#include <string>
 15#include <cmath>
 16#include <cstdlib>
 17#include <ctime>
 18#define fst first
 19#define sec second
 20#define lson l,m,rt<<1
 21#define rson m+1,r,rt<<1|1
 22#define ms(a,x) memset(a,x,sizeof(a))
 23typedef long long LL;
 24#define pi pair < int ,int >
 25#define MP make_pair
 26using namespace std;
 27const double eps = 1E-8;
 28const int dx4[4]={1,0,0,-1};
 29const int dy4[4]={0,-1,1,0};
 30const int inf = 0x3f3f3f3f;
 31const int N=2E5+7;
 32char s[N];
 33int n,sa[N],rk[N],t[N],t2[N],cnt[N];
 34int height[N];
 35int cmp(int *r,int a,int b,int l)  {return r[a]==r[b]&&r[a+l]==r[b+l];}
 36void getSa(int n,int m)
 37{
 38    int *x = t,*y= t2;
 39    ms(cnt,0);
 40    for ( int i = 0 ; i < n ; i++) cnt[x[i]=s[i]]++;
 41    for ( int i = 1 ; i < m ; i++) cnt[i]+=cnt[i-1];
 42    for ( int i = n-1 ; i >= 0 ; i--) sa[--cnt[x[i]]] =  i;
 43    for ( int k = 1 ; k <= n ;  k<<=1)
 44    {
 45	int p = 0 ;
 46	for ( int i = n - k ; i < n ; i++) y[p++] = i;
 47	for ( int i =  0 ; i < n ; i++) if (sa[i]>=k) y[p++] = sa[i]-k;
 48	ms(cnt,0);
 49	for ( int i = 0 ; i < n;  i++) cnt[x[y[i]]]++;
 50	for ( int i = 0 ; i < m ; i++) cnt[i]+=cnt[i-1];
 51	for ( int i = n-1 ; i >= 0 ; i--) sa[--cnt[x[y[i]]]] = y[i];
 52	swap(x,y);
 53	p = 1;
 54	x[sa[0]] = 0;
 55	for ( int i = 1 ; i < n ; i++)
 56	    x[sa[i]] = cmp(y,sa[i-1],sa[i],k)?p-1:p++;
 57	if (p>=n) break;
 58	m = p;
 59    }
 60}
 61void getHeight( int n)
 62{
 63    int k = 0 ;
 64    for ( int i = 0 ; i < n ; i++) rk[sa[i]] = i ;
 65    height[0] = 0 ;
 66    for ( int i = 0 ; i < n ; i++)
 67    {
 68	if (rk[i]==0) continue;
 69	if (k) k--;
 70	int j = sa[rk[i]-1];
 71	while (s[i+k]==s[j+k]) k++;
 72	height[rk[i]] = k ;
 73    }
 74}
 75int getSuffix(char s[])
 76{
 77    int len = strlen(s);
 78    int up = 0 ;
 79    for ( int i = 0 ; i < len ; i++)
 80    {
 81	int val = s[i];
 82	up = max(up,val);
 83    }
 84    getSa(len,up+1);
 85    getHeight(len);
 86    return len;
 87}
 88int main()
 89{
 90	#ifndef  ONLINE_JUDGE 
 91	freopen("code/in.txt","r",stdin);
 92  #endif
 93	string st1,st2,st;
 94	int len1,len;
 95	cin>>len1>>st1>>st2;
 96	st = st1+"$"+st2;
 97	strcpy(s,st.c_str());
 98	len = getSuffix(s);
 99	int ans = 0 ,beg=0;
100	for ( int i = 2 ; i < len ; i++)
101	    if (height[i]>ans)
102	    {
103		if (0<=sa[i-1]&&sa[i-1]<len1&&len1<sa[i])
104		{
105		    beg = sa[i-1];
106		    ans = height[i];
107		}
108		if (0<=sa[i]&&sa[i]<len1&&len1<sa[i-1])
109		{
110		    beg = sa[i];
111		    ans = height[i];
112		}
113	    }
114	cout<<st1.substr(beg,ans)<<endl<<endl;
115  #ifndef ONLINE_JUDGE  
116  fclose(stdin);
117  #endif
118    return 0;
119}