Milk Patterns POJ - 3261

 //sa[i]表示排名为i是从sa[i]位置开始的后缀
//rank[i]表示起始位置的下标为i的后缀的排名
// height[i]表示排名相邻的两个后缀的最长公共前缀长度

//参考后缀数组（非常清楚）

https://www.cnblogs.com/victorique/p/8480093.html

//#include<bits/stdc++.h>
#include<iostream>
#include<cstdio>
#include<cstring>

using namespace std;

const int maxn = 200010;

int n, k;
int s[maxn];
int sa[maxn] , rank[maxn] , height[maxn];
int p[maxn] , tmp[maxn] , cnt[maxn];

bool Isequal(int x,int y,int l) {
	return rank[x] == rank[y] && rank[x + l] == rank[y + l];
}

void Get_SA() {
	for(int i = n; i; --i)
		s[i] = s[i - 1];

	for(int i = 1; i <= n; ++i) {
		rank[i] = s[i];
		sa[i] = i;
	}

	for(int l = 0 , pos = 0 , sig = 122; pos < n; sig = pos) {
		pos = 0;

		for(int i = n - l + 1; i <= n; ++i)
			p[++pos] = i;

		for(int i = 1; i <= n; ++i)
			if(sa[i] > l) p[ ++pos ] = sa[i] - l;

		memset( cnt , 0 ,sizeof(int) * (sig + 1));

		for(int i = 1; i <= n; ++i)
			++cnt[rank[i]];

		for(int i = 1; i <= sig; ++i)
			cnt[i] += cnt[i - 1];

		for(int i = n; i; --i)
			sa[cnt[rank[p[i]]] -- ] = p[i];

		pos = 0;

		for(int i = 1; i <= n; ++i)
			tmp[sa[i]] = Isequal(sa[i] , sa[i - 1] , l)?pos:++pos;

		for(int i = 1; i <= n; ++i)
			rank[i] = tmp[i];

		l = !l? 1 : l << 1;
	}
	return;
}

void CalHeight(int *r,int *sa,int n) 
{
//	cout << "starting" << endl;
	for(int i=1,j=1,k=1; i<=n; height[rank[i++]]=k){
		for(k?--k:0, j=sa[rank[i]-1]; r[i+k] == r[j+k]; ++k);
				
//		cout << rank[i] << "=" << k << endl;
	}
}

int main() {
	cin >> n >> k;

	for(int i=0; i<n; i++) {
		cin >> s[i];
	}
	Get_SA();
	
	CalHeight(s, sa, n);

	int l=1, r=n, mid, sum=0, num=1;

	while(l<=r) {
		mid = l+r>>1;
		num=1;

		for(int i=1; i<=n; ++i) {			
			if(height[i] >= mid)
				++num;
			else num=1;

			if(num >= k)
				break;
		}

		if(num>=k)
			l=mid+1;
		else r=mid-1;
	}
	
	cout<<r<<endl;

	return 0;
}