POJ 2019 Cornfields（二维RMQ）

　　相比以前的RMQ不同的是,这是一个二维的ST算法

#include<iostream>
#include<cstring>
#include<cstdio>
#include<cmath>
using namespace std;
#define N 300
int minbest[8][8][N][N];
int maxbest[8][8][N][N];
///int lg[N];
int getmax(int a,int b,int c,int d)
{
    return max(max(a,b),max(c,d));
}
int getmin(int a,int b,int c,int d)
{
    return min(min(a,b),min(c,d));
}
int lg(int x)
{
    if(x == 1) return 0;
    return lg(x>>1) + 1;
}
int main()
{
    int n,b,k;
    while(EOF != scanf("%d%d%d",&n,&b,&k))
    {
        //lg[0] = -1;
        /* for(int i = 1; i <= n; i++)
         if(i&(i-1) == 0)
             lg[i] = lg[i-1] + 1;
         else lg[i] = lg[i-1];*/
        for(int i = 1; i <= n; i++)
        {
            for(int j = 1; j <= n ; j++)
            {
                int num;
                scanf("%d",&num);
                minbest[0][0][i][j] = maxbest[0][0][i][j] = num;
            }
        }
        for(int i = 0; (1<<i) <= n ; i++)
            for(int j = 0; (1<<j) <= n ; j++)
            {
                if(i + j)
                {
                    for(int x = 0; x <= n+1-(1<<i); x++)
                        for(int y = 0; y <= n+1-(1<<j); y++)
                        {
                            if(i)
                            {
                                minbest[i][j][x][y] = min(minbest[i-1][j][x][y],minbest[i-1][j][x+ (1<<i-1)][y]);
                                maxbest[i][j][x][y] = max(maxbest[i-1][j][x][y],maxbest[i-1][j][x+ (1<<i-1)][y]);
                            }
                            if(j)
                            {
                                minbest[i][j][x][y] = min(minbest[i][j-1][x][y],minbest[i][j-1][x][y + (1<<j-1)]);
                                maxbest[i][j][x][y] = max(maxbest[i][j-1][x][y],maxbest[i][j-1][x][y + (1<<j-1)]);
                            }
                        }
                }
            }

        int tmp = lg(b) ;
        ///cout<<tmp<<endl;
        while(k--)
        {
            int x,y;
            scanf("%d%d",&x,&y);
            int mi = getmin(minbest[tmp][tmp][x][y],minbest[tmp][tmp][x+b-(1<<tmp)][y],
                            minbest[tmp][tmp][x][y+b-(1<<tmp)],minbest[tmp][tmp][x+b-(1<<tmp)][y+b-(1<<tmp)]
                           );
            int ma = getmax(maxbest[tmp][tmp][x][y],maxbest[tmp][tmp][x+b-(1<<tmp)][y],
                            maxbest[tmp][tmp][x][y+b-(1<<tmp)],maxbest[tmp][tmp][x+b-(1<<tmp)][y+b-(1<<tmp)]
                           );
            ///cout<<ma<<"   "<<mi<<endl;
            printf("%d
",ma - mi);
        }
    }
    return 0;
}