of binary tree we can draw binary tree with an algorithm that assigns xand -coordinates to node of using the following two rules (see figure ) (vis the number of nodes visited before in the inorder traversal of (vis the depth of in in this applicationwe take the convention common in computer graphics that xcoordinates increase left to right and -coordinates increase top to bottom so the origin is in the upper left corner of the computer screen figure an inorder drawing of binary tree the euler tour traversal of binary tree the tree-traversal algorithms we have discussed so far are all forms of iterators each traversal visits the nodes of tree in certain orderand is guaranteed to visit each node exactly once we can unify the tree-traversal algorithms given above into single frameworkhoweverby relaxing the requirement that each node be visited exactly once the resulting traversal method is called the euler tour traversalwhich we study next the advantage of this traversal is that it allows for more general kinds of algorithms to be expressed easily the euler tour traversal of binary tree can be informally defined as "walkaround twhere we start by going from the root toward its left childviewing the edges of as being "wallsthat we always keep to our left (see figure each node of is encountered three times by the euler tour"on the left(before the euler tour of ' left subtree"from below(between the euler tours of ' two subtrees"on the right(after the euler tour of ' right subtree