用於ProjectEuler問題的程序優化11

Question

我一直在學習編程相當多，看起來程序員之間最大的競爭之一就是可以在多少行內完成一個過程。注意到這個趨勢， d喜歡學習使我的程序更緊湊，更清潔，並且更喜歡沒有多餘的功能。這裏是我用來解決ProjectEuler問題11的代碼。當我看到代碼的四分之一大小做同樣的事情時，它會非常大，這讓我很擔心，呵呵。

#include <iostream> 

using namespace std; 

int array[20][20] = {{8,2,22,97,38,15,0,40,0,75,4,5,7,78,52,12,50,77,91,8}, 
         {49,49,99,40,17,81,18,57,60,87,17,40,98,43,69,48,4,56,62,0}, 
         {81,49,31,73,55,79,14,29,93,71,40,67,53,88,30,3,49,13,36,65}, 
         {52,70,95,23,4,60,11,42,69,24,68,56,1,32,56,71,37,2,36,91}, 
         {22,31,16,71,51,67,63,89,41,92,36,54,22,40,40,28,66,33,13,80}, 
         {24,47,32,60,99,3,45,2,44,75,33,53,78,36,84,20,35,17,12,50}, 
         {32,98,81,28,64,23,67,10,26,38,40,67,59,54,70,66,18,38,64,70}, 
         {67,26,20,68,2,62,12,20,95,63,94,39,63,8,40,91,66,49,94,21}, 
         {24,55,58,5,66,73,99,26,97,17,78,78,96,83,14,88,34,89,63,72}, 
         {21,36,23,9,75,0,76,44,20,45,35,14,0,61,33,97,34,31,33,95}, 
         {78,17,53,28,22,75,31,67,15,94,3,80,4,62,16,14,9,53,56,92}, 
         {16,39,5,42,96,35,31,47,55,58,88,24,0,17,54,24,36,29,85,57}, 
         {86,56,0,48,35,71,89,7,5,44,44,37,44,60,21,58,51,54,17,58}, 
         {19,80,81,68,5,94,47,69,28,73,92,13,86,52,17,77,4,89,55,40}, 
         {4,52,8,83,97,35,99,16,7,97,57,32,16,26,26,79,33,27,98,66}, 
         {88,36,68,87,57,62,20,72,3,46,33,67,46,55,12,32,63,93,53,69}, 
         {4,42,16,73,38,25,39,11,24,94,72,18,8,46,29,32,40,62,76,36}, 
         {20,69,36,41,72,30,23,88,34,62,99,69,82,67,59,85,74,4,36,16}, 
         {20,73,35,29,78,31,90,1,74,31,49,71,48,86,81,16,23,57,5,54}, 
         {1,70,54,71,83,51,54,69,16,92,33,48,61,43,52,1,89,19,67,48}, 
         }; 

int s = 0; 

int right() 
{ 
    int a = 1; 
    int i = 0; 
    int n = 0; 
    int r = 0; 
    int c = 0; 

    for(n = 0;n <= 359;n++) 
    { 
     if(c <= 16) 
     { 
      for(i = 0;i <= 3;i++) 
      { 
       //cout << " " << array[r][(c + i)] << " "; 
       a *= array[r][(c + i)]; 
      }; 
      //cout << a << " "; 
      i = 0; c++; 
      if(a > s) 
      { 
       s = a; 
       a = 1; 
      }; 
      //cout << s << " " << endl; 
      a = 1; 
     }else{c = 0; r++;}; 
    }; 

    return s; 
}; 

int left() 
{ 
    int a = 1; 
    int i = 0; 
    int n = 0; 
    int r = 0; 
    int c = 19; 

    for(n = 0;n <= 359;n++) 
    { 
     if(c >= 3) 
     { 
      for(i = 0;i <= 3;i++) 
      { 
       //cout << " " << array[r][(c - i)] << " "; 
       a *= array[r][(c - i)]; 
      }; 
      //cout << a << " "; 
      i = 0; c--; 
      if(a > s) 
      { 
       s = a; 
       a = 1; 
      }; 
      //cout << s << " " << endl; 
      a = 1; 
     }else{c = 19; r++;}; 
    }; 

    return s; 
}; 

int down() 
{ 
    int n = 0; 
    int i = 0; 
    int r = 0; 
    int c = 0; 
    int a = 1; 

    for(n = 0;n <= 356;n++) 
    { 
     if(c <= 19) 
     { 
      for(i = 0;i <= 3;i++) 
      { 
       //cout << " " << array[(r + i)][c] << " "; 
       a *= array[(r + i)][c]; 
      }; 
      //cout << a << " "; 
      i = 0; c++; 

      if(a > s) 
      { 
       s = a; 
       a = 1; 
      }; 
      //cout << s << " " << endl; 
      a = 1; 
     }else{c = 0; 
       if(r <= 16){ 
        r++; 
        }else{break;}; 
     }; 
    }; 

    return s; 
}; 

int up() 
{ 
    int n = 0; 
    int i = 0; 
    int r = 19; 
    int c = 0; 
    int a = 1; 

    for(n = 0;n <= 356;n++) 
    { 
     if(c <= 19) 
     { 
      for(i = 0;i <= 3;i++) 
      { 
       //cout << " " << array[(r - i)][c] << " "; 
       a *= array[(r - i)][c]; 
      }; 
      //cout << a << " "; 
      i = 0; c++; 

      if(a > s) 
      { 
       s = a; 
       a = 1; 
      }; 
      //cout << s << " " << endl; 
      a = 1; 
     }else{c = 0; 
       if(r >= 3){ 
        r--; 
        }else{break;}; 
     }; 
    }; 

    return s; 
}; 

int diag_left_up() 
{ 
    int n = 0; 
    int i = 0; 
    int r = 19; 
    int c = 19; 
    int a = 1; 

    for(n = 0;n <= 304;n++) 
    { 
     if(c >= 3 && r >= 3) 
     { 
      for(i = 0;i <= 3;i++) 
      { 
       //cout << " " << array[(r - i)][(c - i)] << " "; 
       a *= array[(r - i)][(c - i)]; 
      }; 
      //cout << a << " "; 
      i = 0; c--; 

      if(a > s) 
      { 
       s = a; 
       a = 1; 
      }; 
      //cout << s << " " << endl; 
      a = 1; 
     }else{c = 19; 
       if(r >= 3){ 
        r--; 
        }else{break;}; 
     }; 
    }; 

    return s; 
}; 

int diag_left_down() 
{ 
    int n = 0; 
    int i = 0; 
    int r = 0; 
    int c = 19; 
    int a = 1; 

    for(n = 0;n <= 304;n++) 
    { 
     if(c >= 3 && r <= 16) 
     { 
      for(i = 0;i <= 3;i++) 
      { 
       //cout << " " << array[(r + i)][(c - i)] << " "; 
       a *= array[(r + i)][(c - i)]; 
      }; 
      //cout << a << " "; 
      i = 0; c--; 

      if(a > s) 
      { 
       s = a; 
       a = 1; 
      }; 
      //cout << s << " " << endl; 
      a = 1; 
     }else{c = 19; 
       if(r <= 16){ 
        r++; 
        }else{break;}; 
     }; 
    }; 

    return s; 
}; 

int diag_right_up() 
{ 
    int n = 0; 
    int i = 0; 
    int r = 19; 
    int c = 0; 
    int a = 1; 

    for(n = 0;n <= 304;n++) 
    { 
     if(c <= 16 && r >= 3) 
     { 
      for(i = 0;i <= 3;i++) 
      { 
       //cout << " " << array[(r - i)][(c + i)] << " "; 
       a *= array[(r - i)][(c + i)]; 
      }; 
      //cout << a << " "; 
      i = 0; c++; 

      if(a > s) 
      { 
       s = a; 
       a = 1; 
      }; 
      //cout << s << " " << endl; 
      a = 1; 
     }else{c = 0; 
       if(r >= 3){ 
        r--; 
        }else{break;}; 
     }; 
    }; 

    return s; 
}; 

int diag_right_down() 
{ 
    int n = 0; 
    int i = 0; 
    int r = 0; 
    int c = 0; 
    int a = 1; 

    for(n = 0;n <= 304;n++) 
    { 
     if(c <= 16 && r <= 16) 
     { 
      for(i = 0;i <= 3;i++) 
      { 
       //cout << " " << array[(r + i)][(c + i)] << " "; 
       a *= array[(r + i)][(c + i)]; 
      }; 
      //cout << a << " "; 
      i = 0; c++; 

      if(a > s) 
      { 
       s = a; 
       a = 1; 
      }; 
      //cout << s << " " << endl; 
      a = 1; 
     }else{c = 0; 
       if(r <= 16){ 
        r++; 
        }else{break;}; 
     }; 
    }; 

    return s; 
}; 

int main() 
{ 
    cout << "Result from right():" << '\t' << right(); 
    cout << endl; 
    cout << "Result from left():" << '\t' << left(); 
    cout << endl; 
    cout << "Result from down():" << '\t' << down(); 
    cout << endl; 
    cout << "Result from up():" << '\t' << up(); 
    cout << endl; 
    cout << "Result from diag_right_up(): " << '\t' << diag_right_up(); 
    cout << endl; 
    cout << "Result from diag_right_down(): " << '\t' << diag_right_down(); 
    cout << endl; 
    cout << "Result from diag_left_up(): " << '\t' << diag_left_up(); 
    cout << endl; 
    cout << "Result from diag_left_down(): " << '\t' << diag_left_down(); 

    cout << endl << endl << "Greatest result: " << s; 

    return 0; 
} 

Answer 1

我注意到的第一件事是，你有很多功能基本上做了同樣的事情（有些數字不同）。我會研究爲該功能添加幾個參數，以便您可以描述您要前往的方向。因此，例如，您可以撥打traverse(1, 0)和traverse(0, -1)而不是up()，而不是撥打right()。

你traverse()函數聲明可能看起來像：

int traverse(int dx, int dy) 

裏面去適應它的dx和dy不同的價值觀的行爲進行適當的修改。

Answer 2

對於初學者來說，你只需要其中的四個方向：右/左，上/下，右上/左下和右下/左上。乘法是可交換的，所以從一個給定的對中去哪個方向並不重要（如果你在一個方向上發現「abcd」，你會在相反的方向上找到「dcba」，並且你可以得到相同的結果數字在一起）。其次，使用更多的描述性變量名稱。像s這樣的變量名是沒有意義的;像maximum這樣的東西比較好，因爲它會告訴你這個變量是什麼。這並不意味着你永遠不應該使用單字符變量名 - 例如，使用i作爲for-loop計數器是非常好的，如果你正在處理座標，那麼x和y也可以很好，但在所有可能的情況下，您應該使用描述性名稱來使代碼更加自我記錄。

第三，您可以查看Greg建議的內容並重構您的方法來代替方向。這將允許你排除全部的類似方法（並且只需使用不同參數調用該方法4次即可覆蓋所有必要的方向）。

最後，您可能希望對格式更加一致 - 我知道這很難開始，但從長遠來看它可以幫助您。要明白我的意思在這裏，需要在這個片段好好看看，從你的down()方法採取：

 if(c <= 19) 
     { 
      for(i = 0;i <= 3;i++) 
      { 
       //cout << " " << array[(r + i)][c] << " "; 
       a *= array[(r + i)][c]; 
      }; 
      //cout << a << " "; 
      i = 0; c++; 

      if(a > s) 
      { 
       s = a; 
       a = 1; 
      }; 
      //cout << s << " " << endl; 
      a = 1; 
     }else{c = 0; 
       if(r <= 16){ 
        r++; 
        }else{break;}; 
     }; 

注意如何在一個地方你的IFS的左花括號之前斷行，但寫}else{線。此外，裏面第一個else，您有另一個if塊，其中不在大括號之前放置換行符，並且右括號具有與塊內容（r++;）相同的縮進級別。這是非常不一致的，並且使其更難閱讀。