hdu 2642 (summerIII J) 二维树状数组

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#include<cstdio>#include<cstring>#include<cmath>using namespace std;const int maxn=4000;int c[maxn][maxn],n;char str[10];int lowbit(int x){    return x&(-x);}void update(int i,int j,int val){   for(int x=i;x<maxn;x+=lowbit(x))    for(int y=j;y<maxn;y+=lowbit(y))   {       c[x][y]+=val;   }}int getsum(int i,int j){   int result=0;   for(int x=i;x>0;x-=lowbit(x))   {       for(int y=j;y>0;y-=lowbit(y)){        result+=c[x][y];       }   }   return result;}int main(){    scanf("%d%*c",&n);    while(n--)    {        scanf("%s",str);        //printf("n:%d\n",n);        if(str[0]=='B')        {            int x,y;            scanf("%d%d%*c",&x,&y);            x++;            y++;            if(getsum(x,y)-getsum(x-1,y)-getsum(x,y-1)+getsum(x-1,y-1)==0)            update(x,y,1);        }        else if(str[0]=='D')        {            int x,y;            scanf("%d%d%*c",&x,&y);            x++;            y++;            if(getsum(x,y)-getsum(x-1,y)-getsum(x,y-1)+getsum(x-1,y-1)==1)//计算某一个点是否亮不能直接用C[][]数组判断，下标不一致，应用getsum来计算。            update(x,y,-1);        }        else if(str[0]=='Q')        {            int x1,x2,y1,y2;            scanf("%d%d%d%d%*c",&x1,&x2,&y1,&y2);            if(x1>x2)            {                int t=x1;                x1=x2;                x2=t;            }            if(y2>y1)            {                int t=y1;                y1=y2;                y2=t;            }//x1 y1,x2,y2的大小不确定，需要先行比较排序。            //printf("1:%d\n",getsum(x2+1,y1+1));            //printf("2:%d\n",getsum(x1+1,y1+1));            //printf("3:%d\n",getsum(x2+1,y2+1));            //printf("4:%d\n",getsum(x1+1,y2+1));            int sum=(getsum(x2+1,y1+1)-getsum(x1,y1+1))-(getsum(x2+1,y2)-getsum(x1,y2));//边界上的点直接做减法会有算不上的，所以把区间点边界点减一，把区间边界点包括进去。            printf("%d\n",sum);        }    }    return 0;}
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