69, b should be the root nodes only left subtree, d for the right subtree is the lower left node, e can not be d ancestor nodes, so can only be d nodes on the lower right, but in the end an analysis of the result tree to draw out the

CodePudding user response:

, write write the possible sequence is arranged in a line, which is simple, but I don't think this class tree I draw the antecedent sequence for abcdfeg the nearest tree