假设自上而下按层次，自左至右输入每个结点的一个三元组(N, P, L/R)。其中N为本结点的元素，P为其父结点，L指示N为P 的左孩子，R指示N为P的右孩子。试写一个建立二元树在内存的双链表示算法，并实现先根、中根、后根以及层序遍历算法。-Assuming top-down by level, each node from left to right input a triple (N, P, L/R). Where the elements of N-based nodes, P is the parent node, L indicates the left child N to P, R N for the P instructions right child. Try to write a build a binary tree in memory of the duplex, said algorithms, and to achieve the first root, the root, root, and the sequence after the traversal algorithm.