Epic - Snake Sequence

You are given a grid of numbers. A snakes equence is made up of adjacent numbers such that for each number, the number on the right or the number below it is +1 or -1 its value. For example, 

1 3 2 6 8 

-9 7 1 -1 2 

1 5 0 1 9 

In this grid, (3, 2, 1, 0, 1) is a snake sequence. Given a grid, find the longest snake sequences and their lengths (so there can be multiple snake sequences with the maximum length).

简单的动态规划，使用一个相同大小的数组记录到snake sequence该点的长度（默认为1），并维护最大值。

def snake(matrix)
  return 0 if matrix.empty?
  m , n = matrix.length, matrix[0].length
  dp = Array.new(m){Array.new(n,1)}
  ans = -1
  m.times do |i|
    n.times do |j|
      dp[i][j] = dp[i-1][j] + 1 if i > 0 and (matrix[i-1][j] - matrix[i][j]).abs == 1
      dp[i][j] = dp[i][j-1] + 1 if j > 0 and (matrix[i][j-1] - matrix[i][j]).abs == 1
      ans = [ans,dp[i][j]].max
    end
  end
  ans
end