ProjectEuler问题11的程序优化

Question

我学习编程已经有相当长的时间了，似乎程序员之间最大的竞争之一就是用很少的几行代码就能完成一个过程。注意到这一趋势，我想学会让我的程序更紧凑，更干净，更喜欢没有多余的功能。这是我用来解决ProjectEuler问题11的代码。它相当大，当我看到四分之一的代码做同样的事情时，我有点担心，哈哈。

#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，你有很多函数做基本上相同的事情(有些数字不同)。我将研究向该函数添加几个参数，这样您就可以描述您正在进行的方向。例如，您可以调用traverse(1, 0)和traverse(0, -1)而不是up()，而不是调用right()。

您的traverse()函数声明可能如下所示：

int traverse(int dx, int dy)

内部进行了适当的更改，以使其行为适应dx和dy的不同值。

Answer 2

首先，你只需要四个方向:右/左，上/下，右上/下左和右下/上左。乘法是可交换的，所以从一个给定的对到哪个方向并不重要(如果你在一个方向上找到"a b c d“，你会在相反的方向上找到"d c b a”，当你把这些数字相乘时，你会得到相同的结果)。

其次，使用更具描述性的变量名称。像s这样的变量名是没有意义的；像maximum这样的名称更好，因为它会告诉您该变量的用途。这并不意味着你永远不应该使用单字符的变量名-例如，使用i作为for循环计数器是完全可以的，如果你正在处理坐标，x和y也可以，但只要有可能，你应该使用一个描述性的名称来使代码更具自我文档化。

第三，你可以看看Greg的建议，然后重构你的方法，转而采取一个方向。这将允许您抛弃所有类似的方法(只需使用不同的参数调用一个方法4次，以涵盖所有必要的方向)。

最后，您可能想要在格式上保持更一致-我知道这很难开始，但从长远来看，这对您很有帮助。要理解我在这里的意思，请仔细看一下摘自down()方法的这段代码：

        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;};
        };

注意你是如何在ifs的大括号前换行的，但是要在一行上写}else{。此外，在第一个块中，还有另一个if- else，其中没有在花括号之前换行，并且结束括号具有与块内容(r++;)相同的缩进级别。这是非常不一致的，并使其更难阅读。

Answer 3

static void largestProduct11() {
    int[][] arr = {
        {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}
    };

    /*
     * |A11 A12 A13 *  *  A1N|
     * |A21 A22 A23 *  *  A2N|
     * |A31 A32 A33       A3N|
     *  *                  *
     *  *                  *
     * |An1 A2N A3N *  *  ANN|
     *
     *    */

    String line;
    int[] temp = new int[4];
    int compre = 1;
    int result = 1;

    for (int i = 0; i < arr.length - 3; i++) { // optimize:- the condition is true 
       // if the remaining index are at least four therefore  the length should be reduced by 
       // three that means only the first 16 members can can satisfy the condition 
        for (int j = 0; j < arr[0].length - 3; j++) {  
            result = arr[i][j] * arr[i + 1][j + 1] * arr[i + 2][j + 2] * arr[i + 3][j + 3];
            if (compre < result) {
                compre = result;
            }

        }
    }
  //
  System.out.println(compre  + " Right sie test  ");
    for (int i = 0; i < arr.length - 3; i++) {
        line = "{";
        for (int j = arr[0].length - 1; j > 3; j--) {
            result = arr[i][j] * arr[i + 1][j - 1] * arr[i + 2][j - 2] * arr[i + 3][j 
 - 3];
            if (compre < result) {
                compre = result;
            }
        }

    }

    System.out.println(compre + " final result");  // solution= 70600674
   
   }