Level order traversal(BFS)
In a complete binary tree, find subtree with maximum level N which has maximum sum of elements.
We can obtain the sum of sub-tree of the binary tree if we visit each node in the level order traversal or breadth first search.
We can find the maximum sum sub-tree of maximum level n by traversing n-1 levels(or uptil last level of tree) of each node and finding their sum.
Finally the the correct sub-tree is the one having maximum sum for level n.
We store the root node of the maximum sub-tree and finally print the sub-tree once again using level order traversal.