用两个变量分别记录当前行的行高和摆放起始位置，线性时间逐行模拟每一行，然后利用公式

\[\text{当前行块数}=\lfloor\dfrac{\text{墙宽}-\text{当前行摆放起始位置}}{\text{砖宽}}\rfloor\]

计算出当前行块数。然后有

\[\text{总占用面积}=\sum_{\text{每一行}}{\text{当前行块数}\times \text{砖长}\times \text{砖宽}}\]

墙面积减去它即为所求。

Code: \(\sout\text{忍住不压行很难吗？——很难。}\)

#include <iostream>
#include <cstdio>
#include <vector>
#include <cmath>
using namespace std;

typedef long long Num;
typedef unsigned long long Unum;
typedef long double Lfloat;
#define Rint register int
#define It iterator
#define Os ostream
#define Is istream
#define Ifs ifstream
#define Ofs ofstream

#define AK_IOI bfw

template<typename T>/*T: integer type*/
void read(T& num)
{
    char ch;int f;num=0;while(1){ch=getchar();if(ch=='-' || (ch>='0'&&ch<='9')) break;} (ch=='-')?(f=-1):(f=1,num+=ch-'0');while(1){ch=getchar();if(!(ch=='-' || (ch>='0'&&ch<='9'))) break; num*=10;num+=ch-'0';} num*=f;
}

struct Square
{
    double len;
    double hei;
    Square():len{0.0},hei{0.0}{ }
    Square(const double &length,const double &height):len{length},hei{height}{ }
    inline double length() const{return len;}
    inline double height() const{return hei;}
    inline double s() const{return len*hei;}
};

inline int calc(const double &offset,const Square &panel,const Square &wall)
{
    double offs=offset;
    offs-=panel.length()/2.0;
    return floor((wall.length()-offs)/panel.length());
}

int main()
{
    /*Init*/ 
    double wallL,wallH,panelL,panelH;
    cin>>wallL>>wallH>>panelL>>panelH;
    Square wall{wallL,wallH},panel{panelL,panelH};
    
    /*StdHeight*/
    double lHeight=wall.hei/2.0;
    double lOffset=panel.len/2.0;
    int cnt=calc(lOffset,panel,wall);
    
    /*Down*/
    while(1)
    {
        lHeight+=panel.hei;
        lOffset+=panel.len/4.0;
        if(lHeight+panel.hei/2.0>wall.hei)
        {
            break;
        }
        else if(lOffset+panel.len/2.0>wall.len)
        {
            break;
        }
        cnt+=calc(lOffset,panel,wall);
        cout<<lHeight<<" "<<lOffset<<" "<<cnt<<endl;
    }
    
    /*Up*/
    lHeight=wall.hei/2.0;
    lOffset=panel.len/2.0;
    while(1)
    {
        lHeight-=panel.hei;
        lOffset+=panel.len/2.0;
        if(lHeight-panel.hei/2.0<0.0)
        {
            break;
        }
        else if(lOffset+panel.len/2.0>wall.len)
        {
            break;
        }
        cnt+=calc(lOffset,panel,wall);
        cout<<lHeight<<" "<<lOffset<<" "<<cnt<<endl;
    }
    
    /*Square*/
    cout<<wall.s()-cnt*panel.s()<<endl;
    return 0;
}