Introduction - If you have any usage issues, please Google them yourself
Suppose a hierarchical top-down, left to right to enter a triple each node (N, P, L/R). Wherein the element N-based node, P is the parent node, L indicates left children to P N, R indicates N for the right child of P. Try to write about a build binary tree representation algorithm chain and achieve first root, root, root and layer after preorder algorithm.