poj 3261 Milk Patterns (最长公共子串，后缀数组)

poj3261

题意：给一个字符串，要求找出至少出现k次的最长重复子串...

思路：后缀数组，然后再次用到了根据height数组对后缀进行分组的套路...二分判定合法性，对于当前的最长长度x,分组使得每组中的height[i]都大于等于x,所不同的是，判定变成了存在一个组，后缀的个数至少为k个（因为这样，就可以对于大于等于k个的后缀，同时取前x长度，得到的就是出现了至少k次且长度为x的前缀）1A,蛤蛤蛤

/* ***********************************************
Author :111qqz
Created Time :2016年08月01日 星期一 01时30分34秒
File Name :code/poj/3261.cpp
************************************************ */
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <string>
#include <cmath>
#include <cstdlib>
#include <ctime>
#define fst first
#define sec second
#define lson l,m,rt<<1
#define rson m+1,r,rt<<1|1
#define ms(a,x) memset(a,x,sizeof(a))
typedef long long LL;
#define pi pair < int ,int >
#define MP make_pair
using namespace std;
const double eps = 1E-8;
const int dx4[4]={1,0,0,-1};
const int dy4[4]={0,-1,1,0};
const int inf = 0x3f3f3f3f;
const int N=2E4+7;
const  int M=2E6+11;
const int C = 5;
int n,sa[N],rk[N],t[N],t2[N],cnt[M];
int height[N];
int s[N];
int k;
int cmp(int *r,int a,int b,int l){ return r[a]==r[b]&&r[a+l]==r[b+l];}
void getSa( int n,int m)
{
    int *x = t;
    int *y = t2;
    ms(cnt,0);
    for ( int i = 0 ; i < n;  i++) cnt[x[i]=s[i]]++;
    for ( int i = 1 ; i < m ; i++) cnt[i]+=cnt[i-1];
    for ( int i = n-1 ; i >= 0 ; i--) sa[--cnt[x[i]]] =  i;
    for ( int k = 1 ; k <= n ; k<<=1)
    {
	int p = 0;
	for ( int i = n-k ; i < n;  i++) y[p++] = i ;
	for ( int i = 0 ; i < n;  i++) if (sa[i]>=k) y[p++] = sa[i]-k;
	ms(cnt,0);
	for ( int i = 0 ; i <n ; i++) cnt[x[y[i]]]++;
	for ( int i = 0 ; i <m ; i++) cnt[i]+=cnt[i-1];
	for ( int i = n-1 ; i >= 0 ; i--) sa[--cnt[x[y[i]]]] = y[i];
	swap(x,y);
	p = 1;
	x[sa[0]] = 0 ;
	for ( int i = 1 ; i < n; i++)
	    x[sa[i]] = cmp(y,sa[i-1],sa[i],k)?p-1:p++;
	if (p>=n) break;
	m = p;
    }
}
void getHeight( int n)
{
    int k = 0 ;
    for ( int i = 0 ; i < n; i++) rk[sa[i]] = i ;
    height[0] =  0;
    for ( int i = 0 ; i < n; i ++)
    {
	if (rk[i]==0) continue;
	if (k) k--;
	int j = sa[rk[i]-1];
	while (s[i+k]==s[j+k]) k++;
	height[rk[i]] = k ;
    }
}
int getSuffix( int s[],int len)
{
    int up = 0 ;
    for ( int i = 0 ; i < len ; i++)
    {
	up = max(up,s[i]);
    }
    s[len++] = 0 ;
    getSa(len,up+1);
    getHeight(len);
    return len;
}
bool check( int x,int k,int n)
{
    int cnt = 1 ;
    for ( int i = 2; i  <= n ; i++)
    {
	if (height[i]>=x&&i<n)
	{
	    cnt++;
	    continue;
	}
	if (cnt>=k) return true;
	cnt = 1;
    }
    return false;
}
int main()
{
	#ifndef  ONLINE_JUDGE 
	freopen("code/in.txt","r",stdin);
  #endif
	scanf("%d %d",&n,&k);
	for ( int i = 0 ; i < n ; i++) scanf("%d",&s[i]),s[i]+=C;
	n = getSuffix(s,n);
//	for ( int i = 0 ; i < n; i++) cout<<"s[i]:"<<s[i]<<endl;
	int l = 1,r = n;
	int ans = 0 ;
	while (l<=r)
	{
	    int mid = (l+r)/2;
	    if (check(mid,k,n))
	    {
		ans = mid;
		l = mid + 1;
	    }
	    else r = mid-1;
	}
	printf("%d\n",ans);
  #ifndef ONLINE_JUDGE  
  fclose(stdin);
  #endif
    return 0;
}