标签：des style http color io os ar for strong
Get Many Persimmon Trees
Time Limit:1000MS Memory Limit:30000KB 64bit IO Format:%I64d
& %I64u
Description
Seiji Hayashi had been a professor of the Nisshinkan Samurai School in the domain of Aizu for a long time in the 18th century. In order to reward him for his meritorious career in education, Katanobu Matsudaira, the lord of the
domain of Aizu, had decided to grant him a rectangular estate within a large field in the Aizu Basin. Although the size (width and height) of the estate was strictly specified by the lord, he was allowed to choose any location for the estate in the field.
Inside the field which had also a rectangular shape, many Japanese persimmon trees, whose fruit was one of the famous products of the Aizu region known as ‘Mishirazu Persimmon‘, were planted. Since persimmon was Hayashi‘s favorite fruit, he wanted to have
as many persimmon trees as possible in the estate given by the lord.
For example, in Figure 1, the entire field is a rectangular grid whose width and height are 10 and 8 respectively. Each asterisk (*) represents a place of a persimmon tree. If the specified width and height of the estate are 4 and 3 respectively, the area surrounded
by the solid line contains the most persimmon trees. Similarly, if the estate‘s width is 6 and its height is 4, the area surrounded by the dashed line has the most, and if the estate‘s width and height are 3 and 4 respectively, the area surrounded by the dotted
line contains the most persimmon trees. Note that the width and height cannot be swapped; the sizes 4 by 3 and 3 by 4 are different, as shown in Figure 1.
Figure 1: Examples of Rectangular Estates
Your task is to find the estate of a given size (width and height) that contains the largest number of persimmon trees.
Output
For each data set, you are requested to print one line containing the maximum possible number of persimmon trees that can be included in an estate of the given size.
大致题意：国王所在的领地有W*H个点，其中n个点处有树， 现在领地上最多允许圈（当然可以少于）大小为S*T的矩形，问最多可圈中多少棵树？
解题思路：枚举起点，用二维树状数组求解。
枚举起点时要注意从行列从S和T开始，直到W和H为止。
用二维树状数组时，要注意update（）每次更新时，c[ ] 加的是1。
AC代码：
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
const int maxn = 102;
int n, w, h, s, t;
int c[maxn][maxn];
int lowbit(int x){ return x&(-x); }
void update(int x,int y){
for(int i=x; i<maxn; i+=lowbit(i))
for(int j=y; j<maxn; j+=lowbit(j))
c[i][j] ++;
}
long long sum(int x, int y){
long long ans = 0;
for(int i=x; i>0; i-=lowbit(i))
for(int j=y; j>0; j-=lowbit(j))
ans += c[i][j];
return ans;
}
int main(){
#ifndef ONLINE_JUDGE
freopen("in.txt", "r", stdin);
#endif
int x, y;
while(~scanf("%d", &n) && n){
scanf("%d%d", &w, &h);
memset(c,0,sizeof(c));
for(int i=1; i<=n; i++){
scanf("%d%d", &x, &y);
update(x, y);
}
scanf("%d%d", &s, &t);
long long ans = 0;
for(int i=s; i<=w; i++) //枚举起点
for(int j=t; j<=h; j++)
ans = max(ans, sum(i, j) - sum(i-s, j) - sum(i, j-t) + sum(i-s, j-t)); //树状数组求区域和
printf("%lld\n", ans);
}
return 0;
}
POJ 2029 Get Many Persimmon Trees （二维树状数组）
标签：des style http color io os ar for strong
原文地址：http://blog.csdn.net/u013446688/article/details/39755313
