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Count Complete Tree Nodes in C++
Suppose we have a complete binary tree, we have to count the number of nodes. So if the tree is like −
So the output will be 6.
To solve this, we will follow these steps
- This will use the recursive approach. This method, countNodes() is taking the root as argument.
- hr := 0 and hl := 0
- create two nodes l and r as root
- while l is not empty
- increase hl by 1
- l := left of l
- while r is not empty
- r := right of r
- increase hr by 1
- if hl = hr, then return (2 ^ hl) – 1
- return 1 + countNodes(left of root) + countNodes(right of root)
Let us see the following implementation to get better understanding −
Example
#include <bits/stdc++.h> using namespace std; class TreeNode{ public: int val; TreeNode *left, *right; TreeNode(int data){ val = data; left = right = NULL; } }; void insert(TreeNode **root, int val){ queue<TreeNode*> q; q.push(*root); while(q.size()){ TreeNode *temp = q.front(); q.pop(); if(!temp->left){ if(val != NULL) temp->left = new TreeNode(val); else temp->left = new TreeNode(0); return; }else{ q.push(temp->left); } if(!temp->right){ if(val != NULL) temp->right = new TreeNode(val); else temp->right = new TreeNode(0); return; } else { q.push(temp->right); } } } TreeNode *make_tree(vector<int> v){ TreeNode *root = new TreeNode(v[0]); for(int i = 1; i<v.size(); i++){ insert(&root, v[i]); } return root; } class Solution { public: int fastPow(int base, int power){ int res = 1; while(power > 0){ if(power & 1) res *= base; base *= base; power >>= 1; } return res; } int countNodes(TreeNode* root) { int hr = 0; int hl = 0; TreeNode* l = root; TreeNode* r = root; while(l){ hl++; l = l->left; } while(r){ r = r->right; hr++; } if(hl == hr) return fastPow(2, hl) - 1; return 1 + countNodes(root->left) + countNodes(root->right); } }; main(){ Solution ob; vector<int> v = {1,2,3,4,5,6,7,8,9,10}; TreeNode *node = make_tree(v); cout << (ob.countNodes(node)); }
Input
[1,2,3,4,5,6,7,8,9,10]
Output
10
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