Asst1

代码说明：

  You are given an n x n grid , a starting position on the grid and a goal location. Each point on the grid is assigned an integer, giving its elevation. It is possible to move from a location to any of its 4 neighbours (except at a boundary). The cost of such a move in 1 the absolute value of the difference in elevation. However, if the difference between two points is greater or equal to 4, this represents an impassible cliff