luogu #2852 Milk Patterns：后缀数组“编程题”

题目描述

Farmer John has noticed that the quality of milk given by his cows varies from day to day. On further investigation, he discovered that although he can’t predict the quality of milk from one day to the next, there are some regular patterns in the daily milk quality.
To perform a rigorous study, he has invented a complex classification scheme by which each milk sample is recorded as an integer between 0 and 1,000,000 inclusive, and has recorded data from a single cow over N (1 ≤ N ≤ 20,000) days. He wishes to find the longest pattern of samples which repeats identically at least K (2 ≤ K ≤ N) times. This may include overlapping patterns – 1 2 3 2 3 2 3 1 repeats 2 3 2 3 twice, for example.
Help Farmer John by finding the longest repeating subsequence in the sequence of samples. It is guaranteed that at least one subsequence is repeated at least K times.

输入格式：

Line 1: Two space-separated integers: N and K
Lines 2..N+1: N integers, one per line, the quality of the milk on day i appears on the ith line.

输出格式：

Line 1: One integer, the length of the longest pattern which occurs at least K times

这道题的题意大概是，给定一个串，求至少出现k次的字串的最大长度。
从题面来看，小中取大，明显是二分答案。
我们建好sa后，还需要一个height数组，表示sa[i]和sa[i-1]的最长前缀（O(n)即可求出）
由height数组的定义可知，设当前答案为x，若height数组有连续k-1个大于等于x的树（仔细想想，为什么是k-1），该答案即可行。
时间复杂度O(nlogn)，当然还有RMQ强行O(n)的。

#include
#include
#include
#define maxn 1000050
int t[maxn],sa[maxn],x[maxn],y[maxn],p,m=maxn-49,n,rank[maxn],h[maxn],l,r,mid,k=0,s[maxn],kk; 
using namespace std;
inline void buildsa()
{
    s[n++]=0;
    for (int i=0;i=0;i--) sa[--t[s[i]]]=i;
    for (int j=1;p=j) y[p++]=sa[i]-j;     
        for (int i=0;i=0;i--) sa[--t[x[y[i]]]]=y[i];    
        swap(x,y),p=1,x[sa[0]]=0;    
        for (int i=1;i=kk-1) return 1;
    }
    return 0;
}
int main()
{
    scanf("%d%d",&n,&kk);
    for (int i=0;i