the third kind of traversalpostordercontains the three steps arranged in yet another way call itself to traverse the node' left subtree call itself to traverse the node' right subtree visit the node for the tree in figure visiting the nodes with postorder traversal would generate the expression abc+this is called postfix notation it means "apply the last operator in the expression*to the first and second things the first thing is aand the second thing is bcbcmeans "apply the last operator in the expression+to the first and second things the first thing is and the second thing is cso this gives us ( +cin infix inserting this in the original expression abc+(postfixgives us *( +cpostfix note the code in listing contains methods for preorder and postorder traversalsas well as for inorder we won' show the details herebut you can fairly easily construct tree like that in figure using postfix expression as input the approach is analogous to that of evaluating postfix expressionwhich we saw in the postfix java program (listing in howeverinstead of storing operands on the stackwe store entire subtrees we read along the postfix string as we did in postfix java here are the steps when we encounter an operand make tree with one node that holds the operand push this tree onto the stack here are the steps when we encounter an operator pop two operand trees and off the stack create new tree with the operator in its root attach as the right child of attach as the left child of push the resulting tree back on the stack