二维树状数组练习 POJ 2029

 关于二维树状数组请参看:http://128kj.iteye.com/blog/1746732
poj2029题意：
在一块h*w的地上,有n棵柿子树,划t*s的一块矩形地,使得其划到的柿子树最多,输出最多的数量.

样例:
16 //有多少棵树
10 8 //地的规模h*w
2 2 //(2,2)处有一棵树
2 5
2 7
3 3
3 8
4 2
4 5
4 8
6 4
6 7
7 5
7 8
8 1
8 4
9 6
10 3
4 3 //划t*s的一块地,这里是t和s
8
6 4
1 2
2 1
2 4
3 4
4 2
5 3
6 1
6 2
3 2
0

很明显的二维树状数组,穷举t*s的所有位置,并记录其划到的树的个数和最大值.

下面是AC代码:

import java.util.Scanner;
public class Main{
static final int N=102;
int C[][];//二维树状数组
int w;
int h ;

private int lowbit(int x ){
return x & ( -x );
}

private void Modify( int x , int y , int c ){
for (int i = x ; i <= w ; i+= lowbit( i ))
for (int j = y ; j <= h ; j+= lowbit( j ))
C[i][j] += c ;
}

private int Sum (int x , int y ){
int result = 0 ;
for ( int i = x ; i > 0 ; i -= lowbit( i ))
for ( int j = y ; j > 0 ; j -= lowbit( j ))
result += C[i][j] ;
return result ;
}

public static void main(String[] args){
Main ma=new Main();
ma.go();
}

private void go(){
Scanner in=new Scanner(System.in);
int n , x , y;
while(true) {
n=in.nextInt();
if(n==0) break;
w=in.nextInt();
h=in.nextInt();
C=new int[w+1][h+1];
for (int i = 0 ; i < n ; i++ ){
x=in.nextInt();
y=in.nextInt();
Modify(x,y,1 );//将原矩阵(x,y)处的值设置为1,并更新二维树状数组
}
x=in.nextInt();
y=in.nextInt();
int maxx = -1 ;
int sx=0;
for (int i = x ; i <= w ; i++ )
{
for (int j = y ; j <= h ; j++ )
{
sx = Sum (i,j) + Sum (i-x,j-y)-Sum(i-x,j)-Sum(i,j- y );
if ( sx > maxx )
maxx = sx ;
}
}
System.out.println(maxx);
}
}
}

import java.util.Scanner;
public class Main{
 static final int N=102;
 int C[][];//二维树状数组
 int w;
 int h ;

  private int lowbit(int x ){
    return x & ( -x );
  }

  private void Modify( int x , int y , int c ){
    for (int i = x ; i <= w ; i+= lowbit( i ))
      for (int j = y ; j <= h ; j+= lowbit( j ))
        C[i][j] += c ;
  }

  private   int Sum (int x , int y ){
    int result = 0 ;
    for ( int i = x ; i > 0 ; i -= lowbit( i ))
      for ( int j = y ; j > 0 ; j -= lowbit( j ))
        result += C[i][j] ;
    return result ;
  }

  public static void main(String[] args){
       Main ma=new Main();
       ma.go();
  }
  
   private void go(){
    Scanner in=new Scanner(System.in);
    int n , x , y;
    while(true) {
      n=in.nextInt();
      if(n==0) break;
      w=in.nextInt();
      h=in.nextInt();
      C=new int[w+1][h+1];
      for (int i = 0 ; i < n ; i++ ){
           x=in.nextInt();
           y=in.nextInt();
          Modify(x,y,1 );//将原矩阵(x,y)处的值设置为1,并更新二维树状数组
        }
       x=in.nextInt();
       y=in.nextInt();
       int maxx = -1 ;
       int sx=0;
        for (int  i = x ; i <= w ; i++ )
        {
            for (int j = y ; j <= h ; j++ )
            {
                 sx = Sum (i,j) + Sum (i-x,j-y)-Sum(i-x,j)-Sum(i,j- y );
                if ( sx > maxx )
                maxx = sx ;
            }
        }
       System.out.println(maxx);
    }
  }
}