设计说明：1。数据结构和表示：程序用1、2、3、4分别表示将右、上、左、下的数字块移动到空格之中。采用典型的树+链表结构，每种局面产生一个BoardState类。出于避免走法顺序列表被过多复制的考虑，在树结构中保存局面的继承关系。每种新的局面产生后，引用估值函数产生f的值，再根据大小将其插入链表之中，以便实现“优先展开f值小的节点”。Solve()函数在成功解决问题之后保存一个走法序列供输出并返回零，而失败则返回失败处的节点层数。(具体的判断方法见后文)-Design Notes : 1. Data structure and said : 1,2,3,4 procedures used were said to the right, and left, The figure moved to the block among the blanks. A typical tree Chain structure, each have a situation BoardState category. For France order to avoid excessive copying the list was, in consideration of the tree structure to preserve the situation in relation to the succession. Each of the new situation after the election, have cited valuation function f value, in accordance with the size of its insertion Chain, in order to achieve the "priority start small f value of the node." Solve () function in the successful solution of the problem after a law to preserve sequence for output and return to zero. and failure to return to the failed node floors. (Specific judgment method, see be