Problem 11 Largest product in a grid

Problem 11 Largest product in a grid

https://projecteuler.net/problem=11

In the 20×20 grid below, four numbers along a diagonal line have been marked in red.

08 02 22 97 38 15 00 40 00 75 04 05 07 78 52 12 50 77 91 08
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 08 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 09 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 09 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 08 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 08 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

The product of these numbers is 26 × 63 × 78 × 14 = 1788696.

What is the greatest product of four adjacent numbers in the same direction (up, down, left, right, or diagonally) in the 20×20 grid?

题意：相同方向（上，下，左，右或对角）的四个相邻数字的最大乘积是多少？

从行、列、左斜、右斜四个方向进行遍历。

c++

#include<iostream>
using namespace std;
#define N 20
int main(){
  int a[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 maxx = 0;
  for (int i = 0; i <= 16; i++)
  {
    for (int j = 0; j <= 16; j++)
	{
      int row = a[i][j] * a[i][j+1] * a[i][j+2] * a[i][j+3];  
      int col = a[j][i] * a[j+1][i] * a[j+2][i] * a[j+3][i]; 
      int lef = a[i][N-j-1] * a[i+1][N-j-2] * a[i+2][N-j-3] * a[i+3][N-j-4];
      int rig = a[i][j] * a[i+1][j+1] * a[i+2][j+2] * a[i+3][j+3]; 
       maxx = max(maxx,max(row,max(col,max(lef,rig))));
    }
  }
  printf("%d\n", maxx);
  return 0;
}