首先理解概念：
前序遍历：访问根结点的操作发生在遍历其左右子树之前。
中序遍历：访问根结点的操作发生在遍历其左右子树之中(间)。
后序遍历：访问根结点的操作发生在遍历其左右子树之后。
eg：后序遍历为DBCEFGHA，中序遍历为EDCBAHFG，求前序遍历（网上例子）
解：首先 看后序遍历DBCEFGHA，A为总根节点
　　然后 寻找中序遍历EDCBAHFG中A位置，则EDCB在A的左枝，HFG在A的右枝；
　　重复前两步，从后序遍历最后一位找，在中序遍历寻找对应点，得出左右分枝...
　　　 最后得到AECDBHGF，再自己验证即可...(First understand the concept:
Preorder traversal: the operation to access the root node occurs before the left and right subtrees are traversed.
Middle order traversal: the operation to access the root node occurs in the left and right subtrees.
Sequential traversal: the operation to access the root node occurs after traversing the left and right subtrees.
Eg: the following sequence traverses to DBCEFGHA, and the sequence traversal is EDCBAHFG, and the preorder traversal (online example)
Solution: first, see the back order traversal DBCEFGHA, A is the total root node.
Then find the middle order traversing the position of A in EDCBAHFG, then EDCB in the left branch of A, and HFG in the right branch of A;
Repeat the first two steps, the last one from the back order traversal, searching the corresponding points in the middle order traversal, and the left and right branches...
Finally, AECDBHGF can be verified by itself.)