Calculates all node points for a complete binary tree

Today in Leetcode, meet a topic, which calculates the number of nodes of a complete binary tree. Share your experience here.

First, you need to fully master what is a fully binary tree?

I think there is one thing to note about the concept of a complete binary tree. Complete binary tree: Except for the last layer, the number of nodes on each layer reaches the maximum, and on the last layer there are only a few junctions on the right. The last layer of the knot must be left-leaning. The main idea is to think of a node as "root node", then, and then determine whether it is full two fork tree, because full two fork tree is calculated very simple 2k-1 (k=1,2,3 "), that is, for a full two fork tree only need to calculate its depth, That is, using a full two fork tree to simplify the calculation of the complete binary tree. Of course, there is also a very simple way, is to traverse each node, at the same time as the traversal of the count, obviously this is not a good way.

First, the implementation of Python is posted.

1 classTreeNode:2     def __init__(self, x):3Self.val =x4Self.left =None5Self.right =None6 7 classSolution:8     #@param {TreeNode} root9     #@return {integer}Ten     def __init__(self): OneSelf.count =0 A  -     defCountnodes (self, root): -         if  notRoot: the             return0 -Ldepth =self.getdepth (root.left) -Rdepth =self.getdepth (root.right) -         ifLdepth = =rdepth: +             return(1 << ldepth) +self.countnodes (root.right) -         Else: +             return(1 << rdepth) +self.countnodes (root.left) A  at     defgetdepth (self, root): -Depth=0 -node =Root -          whilenode: -node =Node.left -Depth + = 1 in      -         returnDepth

Next, the C language implements this algorithm, and the idea is exactly the same as above.

1  structTreeNode {2      intVal;3     structTreeNode *Left ;4     structTreeNode *Right ;5 };6 7 intCountnodes (structtreenode*root) {8     intldepth, rdepth;9 Ten     if(Root = =NULL) { One         return 0; A     } -  -Ldepth = Getdepth (root->Left ); theRdepth = Getdepth (root->Right ); -  -     if(Ldepth = =rdepth) { -         return(1<<ldepth) + countnodes (root->Right ); +     } -     Else{ +         return(1<<rdepth) + countnodes (root->Left ); A     } at } -  - intGetdepth (structtreenode*node) { -     intdepth =0; -  -      while(node) { innode = node->Left ; -depth++; to     } +  -     returndepth; the}

For, the above code must be aware that for (1<<ldepth) and (1<<rdepth) must pay attention to the parentheses, because "+" than "<<" priority.

Calculates all node points for a complete binary tree