HDU 1559 二维树状数组

传送门：HDU 1559

模板题， 注意矩阵sum树状数组求和

AC code:

/*adrui's submission
 *Language : C++
 *Result : Accepted
 *File Name: HDU 3333
 *Favorite : Dragon Balls
 *love : yy
 *Standing in the Hall of Fame
 */

#include
#include
#include
#include
using namespace std;

typedef long long LL;

#define debug 0
#define inf 0x3f3f3f3f
#define M(a, b) memset(a, b, sizeof(a))
#define lowbit(x) (x & (-x))

const int maxn = 1000 + 5;

int m, n, x, y;

LL c[maxn][maxn];

void add(int x, int y, LL v) {

    for (int i = x; i <= m; i += lowbit(i))
        for (int j = y; j <= n; j += lowbit(j)) {
            c[i][j] += v;
        }
}


LL getSum(int x, int y) {
    LL res = 0;

    for (int i = x; i; i -= lowbit(i))
        for (int j = y; j; j -= lowbit(j)) {
            res += c[i][j];
        }

    return res;
}

int main() {
#if debug
    freopen("in.txt", "r", stdin);
#endif //debug

    cin.tie(0);
    cin.sync_with_stdio(false);

    int t;
    LL a;

    cin >> t;

    while (t--) {
        M(c, 0);

        cin >> m >> n >> x >> y;

        for (int i = 1; i <= m; ++i)
            for (int j = 1; j <= n; ++j) {
                cin >> a;
                add(i, j, a);
            }

        LL mx = -inf;
        for (int i = x; i <= m; ++i)
            for (int j = y; j <= n; ++j) {
                LL tmp = getSum(i, j) - getSum(i - x, j) - getSum(i, j - y) + getSum(i - x, j - y);
                mx = max(mx, tmp);
            }

        cout << mx << endl;
    }
    return 0;
}