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Problem 11

Ruby ProjectEuler

上の 20 × 20 の数字のなか、赤くマークされた数字の積は 26 × 63 × 78 × 14 = 1788696 となる。
上下左右斜めのいずれかの方向で連続する4つの数字の積のうち最大のものを求めよ。

Problem 11 - PukiWiki
def horizontal_max(mat)
  ans = mat[0][0]*mat[0][1]*mat[0][2]*mat[0][3]
  (0..19).each{|j|
    (4..19).each{|i|
      if mat[j][i-4] < mat[j][i]
        tmp = mat[j][i-3]*mat[j][i-2]*mat[j][i-1]*mat[j][i]
        ans = [ans , tmp].max
      end
    }
  }
  return ans
end

def vertical_max(mat)
  ans = mat[0][0]*mat[1][0]*mat[2][0]*mat[3][0]
  (0..19).each{|j|
    (4..19).each{|i|
      if mat[i-4][j] < mat[i][j]
        tmp = mat[i-3][j]*mat[i-2][j]*mat[i-1][j]*mat[i][j]
        ans = [ans , tmp].max
      end
    }
  }
  return ans
end

def skew_r_max(mat)
  ans = 0

  (0..16).each{|i|
    (0..16).each{|j|
      tmp = mat[i][j]*mat[i+1][j+1]*mat[i+2][j+2]*mat[i+3][j+3]
      ans = [ans , tmp].max
    }
  }

  return ans
end

def skew_l_max(mat)
  ans = 0

  (0..16).each{|i|
    (3..19).each{|j|
      tmp = mat[i][j]*mat[i+1][j-1]*mat[i+2][j-2]*mat[i+3][j-3]
      ans = [ans , tmp].max
    }
  }

  return ans
end


matrix =[
         [ 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, 3,80,04,62,16,14, 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],
         [88,36,68,87,57,62,20,72,03,46,33,67,46,55,12,32,63,93,53,69],
         [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]
        ]



ans =[horizontal_max(matrix),
      vertical_max(matrix),
      skew_l_max(matrix),
      skew_r_max(matrix)].max

p ans

答え:70600674