摘要： We can number binary trees using the following scheme: The empty tree is numbered 0. The single-node tree is numbered 1. All binary trees having m nodes have numbers less than all those having m+1 nodes. Any binary tree having m nodes with left and right subtrees L and R is numbered n such that all trees having m nodes numbered > n have either Left subtrees numbered higher than L, or A left subtree = L and a right subtree numbered higher than R. 阅读全文