poj 2029

题目：http://poj.org/problem?id=2029

二维树状数组，0(n^2)枚举矩形右下角的坐标即可。

#include <cmath>#include <ctime>#include <iostream>#include <string>#include <vector>#include <cstdio>#include <cstdlib>#include <cstring>#include <queue>#include <map>#include <set>#include <algorithm>#include <cctype>#include <stack>#include <deque>using namespace std;typedef long long LL;#define EPS 10e-9#define INF 0x3f3f3f3f#define REP(i,n) for(int i=0; i<(n); i++)const int maxn = 110;int c[maxn][maxn];int lowbit(int x){ return x&-x;}void add(int x,int y){    while(x<maxn){        int y1=y;        while(y1<maxn){           c[x][y1]+=1; y1+=lowbit(y1);        }        x+=lowbit(x);    }}int sum(int x,int y){    int ret=0;    while(x>0){        int y1=y;        while(y1>0){            ret+=c[x][y1];  y1-=lowbit(y1);        }        x-=lowbit(x);    }    return ret;}int main(){    int n,w,h,s,t,ans,x,y;    while(scanf("%d",&n)!=EOF){         if(n==0) break; ans=0;         memset(c,0,sizeof(c));         scanf("%d%d",&w,&h);         for(int i=0;i<n;i++){             scanf("%d %d",&x,&y);             add(x,y);         }         scanf("%d %d",&s,&t);         for(int i=s;i<=w;i++){             for(int j=t;j<=h;j++){                int temp=sum(i,j);                int x1=i-s;  int y1=j-t;                if(x1>=0){                   temp-=sum(x1,j);                }                if(y1>=0){                   temp-=sum(i,y1);                }                if(x1>=0&&y1>=0){                   temp+=sum(x1,y1);                }                if(temp>ans) {                    ans=temp;               //     printf("this %d %d %d\n",ans,i,j);                }             }         }         printf("%d\n",ans);    }   return 0;}