poj3261

后缀数组+单调队列

注意：后缀数组的所有后缀中包括空串，因此有strlen(s)+1个后缀。

View Code

#include <iostream>

#include <cstdio>

#include <cstdlib>

#include <cstring>

using namespace std;



#define N 20005



struct Elem

{

    int pos, value;

    Elem()

    {}

    Elem(int pp, int vv): pos(pp), value(vv)

    {}

}q[N];



int n, m;

int s[N];

// N > 256

int sa[N], height[N], rank[N], tmp[N], top[N];



void input()

{

    scanf("%d%d", &n, &m);

    for (int i = 0; i < n; i++)

        scanf("%d", &s[i]);

}



void makesa(int n)

{

    // O(N * log N)

    int i, j, len, na;

    na = (n < 256 ? 256 : n);

    memset(top, 0, na * sizeof(int));

    for (i = 0; i < n; i++)

        top[rank[i] = s[i] & 0xff]++;

    for (i = 1; i < na; i++)

        top[i] += top[i - 1];

    for (i = 0; i < n; i++)

        sa[--top[rank[i]]] = i;

    for (len = 1; len < n; len <<= 1)

    {

        for (i = 0; i < n; i++)

        {

            j = sa[i] - len;

            if (j < 0)

                j += n;

            tmp[top[rank[j]]++] = j;

        }

        sa[tmp[top[0] = 0]] = j = 0;

        for (i = 1; i < n; i++)

        {

            if (rank[tmp[i]] != rank[tmp[i - 1]] || rank[tmp[i] + len]

                    != rank[tmp[i - 1] + len])

                top[++j] = i;

            sa[tmp[i]] = j;

        }

        memcpy(rank, sa, n * sizeof(int));

        memcpy(sa, tmp, n * sizeof(int));

        if (j >= n - 1)

            break;

    }

}



void lcp(int n)

{

    // O(4 * N)

    int i, j, k;

    for (j = rank[height[i = k = 0] = 0]; i < n - 1; i++, k++)

        while (k >= 0 && s[i] != s[sa[j - 1] + k])

            height[j] = (k--), j = rank[sa[j] + 1];

}



void push(Elem a, int front, int &rear)

{

    while (rear > front && a.value <= q[rear - 1].value)

        rear--;

    q[rear++] = a;

}



int work()

{

    int front = 0, rear = 0;

    for (int i = 1; i < m; i++)

        push(Elem(i, height[i]), front, rear);

    int ret = q[front].value;

    for (int i = m; i <= n; i++)

    {

        while (front != rear && q[front].pos <= i - m + 1)

            front++;

        push(Elem(i, height[i]), front, rear);

        ret = max(ret, q[front].value);

    }

    return ret;

}



int main()

{

    //freopen("t.txt", "r", stdin);

    input();

    makesa(n + 1);

    lcp(n + 1);

    printf("%d\n", work());

    return 0;

}