Identifying the stateful postorder traversal pattern

The stateful postorder traversal technique is very versatile and can solve a wide variety of binary tree problems. These are generally easy or medium problems where we need to process every node using an aggregated value of some function f  applied to its left and right subtrees, and also update some state variable shared between all nodes with the aggregated value as we traverse. A combination of the aggregated value at the root and the state variables is generally the solution to these problems.

If the problem statement or its solution follows the generic template below, it can be solved by applying the stateful postorder traversal technique.