poj 2029Get Many Persimmon Trees解题报告

二维树状数组：类似于一维的状态下，二维存储的是一个区域内的状态。

#include<iostream>
#include<cstdio>
#include<cstring>
#define N 105
#define lowbit(x) x&-x
using namespace std;
int f[N][N];
void init()
{
    memset(f,0,sizeof(f));
}
int m,n;
void add(int x,int y,int v)
{
    int i,j;
    for(i=x;i<=n;i+=lowbit(i))
    for(j=y;j<=m;j+=lowbit(j))
    f[i][j]+=v;
}
int getsum(int x,int y)
{
    int sum=0;
    int i,j;
    for(i=x;i>=1;i-=lowbit(i))
    for(j=y;j>=1;j-=lowbit(j))
    sum+=f[i][j];
    return sum;
}
int main()
{
    int t;
    int x,y;
    int i,j,temp;
    while(scanf("%d",&t)&&t)
    {
        scanf("%d%d",&n,&m);
        init();
        for(i=0;i<t;i++)
        {
            scanf("%d%d",&x,&y);
            add(x,y,1);
        }
        scanf("%d%d",&x,&y);
        int max=0;
        for(i=x;i<=n;i++)
        for(j=y;j<=m;j++)
        {
            temp=getsum(i,j)-getsum(i,j-y)-getsum(i-x,j)+getsum(i-x,j-y);
            max=max>temp?max:temp;
        }
        printf("%d\n",max);
    }
    return 0;
}