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。

#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;
}