Yifenfei is a romantic guy and he likes to count the stars in the sky.
To make the problem easier,we considerate the sky is a two-dimension plane.Sometimes the star will be bright and sometimes the star will be dim.At first,there is no bright star in the sky,then some information will be given as “B x y” where ‘B’ represent bright and x represent the X coordinate and y represent the Y coordinate means the star at (x,y) is bright,And the ‘D’ in “D x y” mean the star at(x,y) is dim.When get a query as “Q X1 X2 Y1 Y2”,you should tell Yifenfei how many bright stars there are in the region correspond X1,X2,Y1,Y2.
There is only one case.
Input
The first line contain a M(M <= 100000), then M line followed.
each line start with a operational character.
if the character is B or D,then two integer X,Y (0 <=X,Y<= 1000)followed.
if the character is Q then four integer X1,X2,Y1,Y2(0 <=X1,X2,Y1,Y2<= 1000) followed.
Output
For each query,output the number of bright stars in one line.
Sample Input
5
B 581 145
B 581 145
Q 0 600 0 200
D 581 145
Q 0 600 0 200
Sample Output
1
0

题意：在一个平面区域里统计出现星星个数；
分析：注意下标界限和修改区域，二维树状数组入门。。。

#include <bits/stdc++.h>
using namespace std;
typedef long long LL;

const int MAXN = 1000 + 10;
int tree[MAXN][MAXN], vis[MAXN][MAXN]; 

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

inline void update(int x, int y, int val) {
    for(int i = x; i <= MAXN - 5; i += lowbit(i)) {
        for(int j = y; j <= MAXN - 5; j += lowbit(j)) {
            tree[i][j] += val; 
        }
    }
}

inline int query(int x, int y) {
    int sum = 0;
    for(int i = x; i > 0; i -= lowbit(i)) {
        for(int j = y; j > 0; j -= lowbit(j)) {
            sum += tree[i][j]; 
        }
    }
    return sum;
}

int main() {
    int n;
    while(~scanf("%d", &n)) {
        memset(vis, 0, sizeof(vis));
        memset(tree, 0, sizeof(tree)); 
        for(int i = 0; i < n; ++i) {
            char ch; int x, y;
            getchar();
            scanf("%c", &ch);
            if(ch == 'B') {
                scanf("%d %d", &x, &y);
                x++, y++;
                if(vis[x][y]) continue;
                update(x, y, 1);
                vis[x][y] = 1;
            }
            else if(ch == 'Q') {
                int x1, x2, y1, y2;
                scanf("%d %d %d %d", &x1, &x2, &y1, &y2);
                x1++, x2++, y1++, y2++;
                if(x1 < x2) swap(x1, x2);
                if(y1 < y2) swap(y1, y2);
                printf("%d\n", query(x1, y1) - query(x1, y2 - 1) - query(x2 - 1, y1) + query(x2 - 1, y2 - 1));
            }
            else {
                scanf("%d %d", &x, &y);
                x++, y++;
                if(!vis[x][y]) continue;
                update(x, y, -1);
                vis[x][y] = 0;
            }
        }
    }
    return 0;
}