Luogu P2852 [USACO06DEC]牛奶模式Milk Patterns

题目链接 \(Click\) \(Here\)

水题。利用\(Height\)的性质维护一个单调栈即可。

#include <bits/stdc++.h>
using namespace std;

#define LL long long
const int N = 1000010;

int n, m = 1000000, q, s[N], sa[N], tp[N];
int rk[N], _rk[N], bin[N], height[N];

void base_sort () {
    for (int i = 0; i <= m; ++i) bin[i] = 0;
    for (int i = 1; i <= n; ++i) bin[rk[tp[i]]]++;
    for (int i = 1; i <= m; ++i) bin[i] += bin[i - 1];
    for (int i = n; i >= 1; --i) sa[bin[rk[tp[i]]]--] = tp[i];
}

void suffix_sort () {
    for (int i = 1; i <= n; ++i) {
        tp[i] = i;
        rk[i] = s[i];
    }
    base_sort ();
    for (int w = 1; w <= n; w <<= 1) {
        int cnt = 0;
        for (int i = n - w + 1; i <= n; ++i) {
            tp[++cnt] = i;
        }
        for (int i = 1; i <= n; ++i) {
            if (sa[i] > w) {
                tp[++cnt] = sa[i] - w;
            }
        }
        base_sort ();
        memcpy (_rk, rk, sizeof (rk));
        rk[sa[1]] = cnt = 1;
        for (int i = 2; i <= n; ++i) {
            rk[sa[i]] = _rk[sa[i]] == _rk[sa[i - 1]] && _rk[sa[i] + w] == _rk[sa[i - 1] + w] ? cnt : ++cnt;
        }
        if (cnt == n) break;
        m = cnt;
    }
    // printf ("sa : ");for (int i = 1; i <= n; ++i) printf ("%d ", sa[i]); printf ("\n");
}

void get_height () {
    int k = 0;
    for (int i = 1; i <= n; ++i) {
        if (k) k--;
        int j = sa[rk[i] - 1];
        while (s[i + k] == s[j + k]) ++k;
        height[rk[i]] = k; 
    }
    // printf ("height : ");
    // for (int i = 1; i <= n; ++i) {
    // 	printf ("%d ", height[i]);
    // }
    // printf ("\n");
}

int que[N];

int main () {
	cin >> n >> q;
	for (int i = 1; i <= n; ++i) {
	    cin >> s[i];
	}
    suffix_sort ();
    get_height ();
	int head = 1, tail = 0, ans = -0x3f3f3f3f;
	for (int i = 1; i <= n; ++i) {
		while (head <= tail && height[que[tail]] >= height[i]) --tail;
		que[++tail] = i;
		while (head <= tail && i - que[head] >= q - 1) ++head;
		ans = max (ans, height[que[head]]);
	}
	cout << ans << endl;
}