按照某种遍历方式对二叉树进行遍历，可以把二叉树中所有结点排序为一个线性序列。在改序列中，除第一个结点外每个结点有且仅有一个直接前驱结点；除最后一个结点外每一个结点有且仅有一个直接后继结点。这些指向直接前驱结点和指向直接后续结点的指针被称为线索（Thread），加了线索的二叉树称为线索二叉树。-According to some traversal of the binary tree traversal, all nodes in the binary tree sort of a linear sequence. Change sequence, in addition to the first node, each node has one and only one immediate predecessor node　each node except the last node and only one direct successor node. These point to the direct precursor node and point to a direct follow-node pointer called clues (Thread) plus a binary tree called clues clues binary tree.