二维树状数组--子矩阵求和

#include <stdio.h>
#define MAXN 1025

int c[MAXN][MAXN] = {0};
int a[MAXN][MAXN] = {0};

int lowbit(int n)
{
return n & (n ^ (n - 1));
}

void add(int x, int y, int num, int n)
{
for (int i = x; i <= n; i += lowbit(i))
{
for (int j = y; j <= n; j += lowbit(j))
{
c[i][j] += num;
}
}
}

int GetSum(int x, int y)
{
int total = 0;
for (int i = x; i > 0; i -= lowbit(i))
{
for (int j = y; j > 0; j -= lowbit(j))
{
total += c[i][j];
}
}
return total;
}

int query(int x1, int y1, int x2, int y2)
{
return GetSum(x2, y2) - GetSum(x1 - 1, y2) - GetSum(x2, y1 - 1) + GetSum(x1 - 1, y1 -1);
}

int main()
{
int instruct = 0;
int n = 0;
scanf("%d %d", &instruct, &n);
while (true)
{
scanf("%d", &instruct);
int x1 = 0;
int y1 = 0;
int x2 = 0;
int y2 = 0;
int num = 0;
if (1 == instruct)//指令为  将a[x1][y1] + num
{
scanf("%d %d %d", &x1, &y1, &num);
add(x1 + 1, y1 + 1, num, n);
}
else if (2 == instruct)//指令为 求位于x1,y1到x2,y2的子矩阵的和
{

scanf("%d %d %d %d", &x1, &y1, &x2, &y2);
printf("%d\n", query(x1 + 1, y1 + 1, x2 + 1, y2 + 1));
}
else if(3 == instruct)//结束指令
{
break;
}
}
return 0;
}