POJ2029 Get Many Persimmon Trees

  題目鏈接：http://poj.org/problem?id=2029

  二維樹狀數組+容斥

  c[i][j]的意義是(i，j)爲右下角的前綴和

  注意要向上統計，向下修改

  注意區別單點修改與區間修改

  貼代碼

#include<cstdio>
#include<cstring>
using namespace std;
int const maxn=105;
int c[maxn][maxn];
int n,w,h;
int lowbit(int x){
	return x&-x;
}
void add(int x,int y){
	for (int i=x;i<=w;i+=lowbit(i))
		for (int j=y;j<=h;j+=lowbit(j))c[i][j]+=1;
}
int query(int x,int y){
	int sum=0;
	for (int i=x;i>=1;i-=lowbit(i))
		for (int j=y;j>=1;j-=lowbit(j))sum+=c[i][j];
	return sum;
}
int max(int x,int y){
	return x>y?x:y;
}
int main(){
	//freopen("2029.in","r",stdin);
	//freopen("2029.out","w",stdout);
	scanf("%d",&n);
	while (n){
		scanf("%d%d",&w,&h);
		w++;h++;
		memset(c,0,sizeof(c));
		while (n--){
			int x,y;
			scanf("%d%d",&x,&y);
			x++;y++;
			add(x,y);
		}int s,t;
		scanf("%d%d",&s,&t);	
		int ans=0;
		for (int i=s+1;i<=w;i++)
			for (int j=t+1;j<=h;j++) ans=max(ans,query(i,j)-query(i-s,j)-query(i,j-t)+query(i-s,j-t));
		printf("%d\n",ans);
		scanf("%d",&n);
	}
	return 0;
}

【寫的有漏洞的，歡迎路過大神吐槽】

  2017/07/06 22:03:04

  Ending.