poj 3261 Milk Patterns

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分析：sa的板子题之一，比男人八题的musical theme还要稍微简单一点。
先做好sa和height的板子，然后二分长度找答案。
关于如何确定同一个串是否出现k次，我是这么想的：
height[i]数组是中的字符串是以字典序排列的，所以说如果height[k]和height[k + 1]都是大于二分值mid的，而这三个串又是相连的，说明他们的前mid长度的子串是相同的。所以对height扫一遍就可以了。

代码：

/*****************************************************/
//#pragma comment(linker, "/STACK:1024000000,1024000000")
#include <map>
#include <set>
#include <ctime>
#include <stack>
#include <queue>
#include <cmath>
#include <string>
#include <vector>
#include <cstdio>
#include <cctype>
#include <cstring>
#include <sstream>
#include <cstdlib>
#include <iostream>
#include <algorithm>

using namespace std;

#define   offcin        ios::sync_with_stdio(false)
#define   sigma_size    26
#define   lson          l,m,v<<1
#define   rson          m+1,r,v<<1|1
#define   slch          v<<1
#define   srch          v<<1|1
#define   sgetmid       int m = (l+r)>>1
#define   ll            long long
#define   ull           unsigned long long
#define   mem(x,v)      memset(x,v,sizeof(x))
#define   lowbit(x)     (x&-x)
#define   bits(a)       __builtin_popcount(a)
#define   mk            make_pair
#define   pb            push_back
#define   fi            first
#define   se            second

const int    INF    = 0x3f3f3f3f;
const ll     INFF   = 1e18;
const double pi     = acos(-1.0);
const double inf    = 1e18;
const double eps    = 1e-9;
const ll     mod    = 1e9+7;
const int    maxmat = 10;
const ull    BASE   = 133333331;

/*****************************************************/
inline void RI(int &x) {
      char c;
      while((c=getchar())<'0' || c>'9');
      x=c-'0';
      while((c=getchar())>='0' && c<='9') x=(x<<3)+(x<<1)+c-'0';
}
/*****************************************************/

const int maxn = 2e4 + 5;
const int maxm = 1e6 + 5;

int s[maxn];
int rank_sa[maxn], height[maxn];
int sa[maxn], t[maxn], t2[maxn], c[maxm];
int N, K;

// 以字符值数组s构造sa，字符值从0-m-1
void build_sa(int n, int m) {
    int *x = t, *y = t2;
    for (int i = 0; i < m; i ++) c[i] = 0;                
    for (int i = 0; i < n; i ++) c[x[i] = s[i]] ++;
    for (int i = 1; i < m; i ++) c[i] += c[i - 1];          
    for (int i = n - 1; i >= 0; i --) sa[-- c[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;
        for (int i = 0; i < m; i ++) c[i] = 0; 
        for (int i = 0; i < n; i ++) c[x[y[i]]] ++;
        for (int i = 1; i < m; i ++) c[i] += c[i - 1];
        for (int i = n - 1; i >= 0; i --) sa[-- c[x[y[i]]]] = y[i];
        swap(x, y);                              
        p = 1; x[sa[0]] = 0;
        for (int i = 1; i < n; i ++)
            x[sa[i]] = (y[sa[i - 1]] == y[sa[i]] && y[sa[i - 1] + k] == y[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 ++) rank_sa[sa[i]] = i;
    for (int i = 0; i < n; i ++) {
        if (k) k --;
        int j = sa[rank_sa[i] - 1];
        while (s[i + k] == s[j + k]) k ++;
        height[rank_sa[i]] = k;
    }
}

bool judge(int mid, int k) {
    int ans = 0;
    for (int i = 1; i < N; i ++) {
        if (height[i] >= mid) ans ++;
        else ans = 0;
        if (ans >= k - 1) return true;
    }
    return false;
}

void Debug() {
    for (int i = 0; i < N; i ++)
        cout<<height[i]<<" ";
    cout<<endl;
}

int main(int argc, char const *argv[]) {
    while (~scanf("%d%d", &N, &K)) {
        for (int i = 0; i < N; i ++) scanf("%d", s + i);


        build_sa(N, 1e6);
        getHeight(N);

        // Debug();

        int lb = 1, ub = N;
        int ans = 0;
        while (lb <= ub) {
            int mid = (lb + ub) >> 1;
            if (judge(mid, K)) lb = mid + 1, ans = mid;
            else ub = mid - 1;
        }

        printf("%d\n", ans);
    }
    return 0;
}