我正在尝试遍历 20x20 网格并计算产品，但总是得到不正确的结果。你能帮忙发现我的错误吗？

正如 MRAB 所回答的那样，这很可能是由于数组溢出。

我注意到的另一件事（但由于冗余计算可能不是问题）是这样的：

            if(upRight_diag > firstMax)
                firstMax = upRight_diag;
            else if(up > firstMax)
                firstMax = up;

如果两者都大于firstMax并且恰好是全局最大值up那么您将错过它。 但这很奇怪，因为up是多余的（由前面的down处理）。

我要作一些一般性评论。 首先，为什么要在向上/向下测试中多次循环？ 您甚至没有使用循环变量。 你只是想测试边界（事实上你没有这样做）。 此外，当您已经在计算right时，无需计算left。 与我已经提到的up和down相同。

下面是计算水平、垂直和两个对角线的简化：

for(int i = 0; i < 20; i++)
{
    for(int j = 0; j < 20; j++)
    {
        int horz=0, vert=0, diagDR=0, diagUR=0;
        if( j >= 3 )
            horz = grid[i][j-3]*grid[i][j-2]*grid[i][j-1]*grid[i][j];
        if( i >= 3 )
            vert = grid[i-3][j]*grid[i-2][j]*grid[i-1][j]*grid[i][j];
        if( i >= 3 && j >= 3 ) {
            diagDR = grid[i-3][j-3]*grid[i-2][j-2]*grid[i-1][j-1]*grid[i][j];
            diagUR = grid[i-3][j]*grid[i-2][j-1]*grid[i-1][j-2]*grid[i][j-3];
        }
        if( horz > absoluteMax ) absoluteMax = horz;
        if( vert > absoluteMax ) absoluteMax = vert;
        if( diagDR > absoluteMax ) absoluteMax = diagDR;
        if( diagUR > absoluteMax ) absoluteMax = diagUR;
    }
}

更笼统（不要假设它总是连续 4 个，或者总是 20 个）。 http://codepad.org/YkrT72kR 我得到了

70600674 （3,15） 处，对角线左下角线

#include <iostream>
#include <inttypes.h>
const uint8_t HEIGHT = 20;
const uint8_t WIDTH = 20;
const uint8_t CONSECUTIVE = 4;
const int GRID[HEIGHT][WIDTH] =
    {{8, 02, 22, 97, 38, 15, 00, 40, 00, 75, 04, 05, 07, 78, 52, 12, 50, 77, 91, 8},
    {49, 49, 99, 40, 17, 81, 18, 57, 60, 87, 17, 40, 98, 43, 69, 48, 04, 56, 62, 00},
    {81, 49, 31, 73, 55, 79, 14, 29, 93, 71, 40, 67, 53, 88, 30, 03, 49, 13, 36, 65},
    {52, 70, 95, 23, 04, 60, 11, 42, 69, 24, 68, 56, 01, 32, 56, 71, 37, 02, 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, 03, 45, 02, 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, 02, 62, 12, 20, 95, 63, 94, 39, 63, 8, 40, 91, 66, 49, 94, 21},
    {24, 55, 58, 05, 66, 73, 99, 26, 97, 17, 78, 78, 96, 83, 14, 88, 34, 89, 63, 72},
    {21, 36, 23, 9, 75, 00, 76, 44, 20, 45, 35, 14, 00, 61, 33, 97, 34, 31, 33, 95},
    {78, 17, 53, 28, 22, 75, 31, 67, 15, 94, 03, 80, 04, 62, 16, 14, 9, 53, 56, 92},
    {16, 39, 05, 42, 96, 35, 31, 47, 55, 58, 88, 24, 00, 17, 54, 24, 36, 29, 85, 57},
    {86, 56, 00, 48, 35, 71, 89, 07, 05, 44, 44, 37, 44, 60, 21, 58, 51, 54, 17, 58},
    {19, 80, 81, 68, 05, 94, 47, 69, 28, 73, 92, 13, 86, 52, 17, 77, 04, 89, 55, 40},
    {04, 52, 8, 83, 97, 35, 99, 16, 07, 97, 57, 32, 16, 26, 26, 79, 33, 27, 98, 66},
    {88, 36, 68, 87, 57, 62, 20, 72, 03, 46, 33, 67, 46, 55, 12, 32, 63, 93, 53, 69},
    {04, 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, 04, 36, 16},
    {20, 73, 35, 29, 78, 31, 90, 01, 74, 31, 49, 71, 48, 86, 81, 16, 23, 57, 05, 54},
    {01, 70, 54, 71, 83, 51, 54, 69, 16, 92, 33, 48, 61, 43, 52, 01, 89, 19, 67, 48}};
int main()
{
    uint64_t max = 0, temp_max = 0;
    uint16_t max_x=0, max_y=0;
    std::string direction = "";
    for (uint8_t i=0; i<HEIGHT; i++)
    {
        for (uint8_t j=0; j<WIDTH; j++)
        {
            // Can we check right?
            if (j < (WIDTH - CONSECUTIVE))
            {
                temp_max=1;
                for (int k=0; k<CONSECUTIVE; k++)
                {
                    temp_max *= GRID[i][j+k];
                }
                if (temp_max > max)
                {
                    max = temp_max;
                    max_x = j;
                    max_y = i;
                    direction = "right";
                }
            }
            // Can we check down?
            if (i < (WIDTH - CONSECUTIVE))
            {
                temp_max=1;
                for (int k=0; k<CONSECUTIVE; k++)
                {
                    temp_max *= GRID[i+k][j];
                }
                if (temp_max > max)
                {
                    max = temp_max;
                    max_x = j;
                    max_y = i;
                    direction = "down";
                }
            }
            // Can we check down-right?
            if ((i < (HEIGHT - CONSECUTIVE)) && (j < (WIDTH - CONSECUTIVE)))
            {
                temp_max=1;
                for (int k=0; k<CONSECUTIVE; k++)
                {
                    temp_max *= GRID[i+k][j+k];
                }
                if (temp_max > max)
                {
                    direction = "diagonal down right";
                    max = temp_max;
                    max_x = j;
                    max_y = i;
                }
            }
            // Can we check up-right?
            if ((i > (CONSECUTIVE)) && (j < (WIDTH - CONSECUTIVE)))
            {
                temp_max=1;
                for (int k=0; k<CONSECUTIVE; k++)
                {
                    temp_max *= GRID[i-k][j+k];
                }
                if (temp_max > max)
                {
                    direction = "diagonal up right";
                    max = temp_max;
                    max_x = j;
                    max_y = i;
                }
            }
        }
    }
    std::cout << "Max product was " << max << " at (" << max_x << "," << max_y << ") in direction " << direction << std::endl;
    return 0;
}

不错的小挑战。 请记住，检查向上，向左，向左诊断，向右诊断是不必要的。 如前所述，始终检查数组边界

这是因为您没有检查数组边界。

例如，当 i 为 19 且 j 为 0 时，您将有 downRight_diag = grid[19][0]*grid[20][1]*grid[21][2]*grid[22][3]; ，但grid定义为 int grid[20][20] 。