poj2019

dp

利用单调双向队列。类似sliding windows。

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#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
using namespace std;

#define maxn 260

struct Node
{
    int pos, a;
    Node()
    {
    }
    Node(int pp, int aa) :
        pos(pp), a(aa)
    {
    }
} q[maxn];

int n, sub, m;
int f[maxn][maxn], fmax[maxn][maxn], fmin[maxn][maxn];
int lmax[maxn][maxn], lmin[maxn][maxn];
int front, rear;

int ins1(Node x)
{
    while (front < rear && x.pos - q[front].pos >= sub)
        front++;
    while (front < rear && x.a > q[rear - 1].a)
        rear--;
    q[rear++] = x;
    return q[front].a;
}

int ins2(Node x)
{
    while (front < rear && x.pos - q[front].pos >= sub)
        front++;
    while (front < rear && x.a < q[rear - 1].a)
        rear--;
    q[rear++] = x;
    return q[front].a;
}

void input()
{
    scanf("%d%d%d", &n, &sub, &m);
    for (int i = 0; i < n; i++)
        for (int j = 0; j < n; j++)
            scanf("%d", &f[i][j]);
}

void work()
{
    for (int i = 0; i < n; i++)
    {
        front = rear = 0;
        for (int j = 0; j < sub - 1; j++)
            ins1(Node(j, f[i][j]));
        for (int j = sub - 1; j < n; j++)
            lmax[i][j] = ins1(Node(j, f[i][j]));
    }
    for (int i = sub - 1; i < n; i++)
    {
        front = rear = 0;
        for (int j = 0; j < sub - 1; j++)
            ins1(Node(j, lmax[j][i]));
        for (int j = sub - 1; j < n; j++)
            fmax[j][i] = ins1(Node(j, lmax[j][i]));
    }

    for (int i = 0; i < n; i++)
    {
        front = rear = 0;
        for (int j = 0; j < sub - 1; j++)
            ins2(Node(j, f[i][j]));
        for (int j = sub - 1; j < n; j++)
            lmin[i][j] = ins2(Node(j, f[i][j]));
    }
    for (int i = sub - 1; i < n; i++)
    {
        front = rear = 0;
        for (int j = 0; j < sub - 1; j++)
            ins2(Node(j, lmin[j][i]));
        for (int j = sub - 1; j < n; j++)
            fmin[j][i] = ins2(Node(j, lmin[j][i]));
    }

}

int main()
{
    //freopen("t.txt", "r", stdin);
    input();
    work();
    for (int i = 0; i < m; i++)
    {
        int a, b;
        scanf("%d %d", &a, &b);
        a = a + sub - 2;
        b = b + sub - 2;
        printf("%d\n", fmax[a][b] - fmin[a][b]);
    }
    return 0;
}