資料結構與演算法(A)

(5 points) A typical dynamic programming example is the snake sequence. Given a grid of numbers, find the maximum length snake sequence. A snake sequence is made up of adjacent numbers in the grid such that for each number, the number on the right or the number below it is $+1$ or $-1$ its value. At location $(x, y)$, you can move right $(x+1, y)$ or move down $(x, y+1)$ if that number is $\pm 1$. The length of a snake sequence is defined as the number of moves. Given the following grid ($M$ rows, $N$ columns; rows top-to-bottom):

9, 6, 5, 2
8, 7, 6, 5
7, 3, 1, 6
1, 1, 1, 7

The maximum LENGTH of snake sequence is?