Given a complete binary tree, count the number of nodes.
Note:
Definition of a complete binary tree from Wikipedia:
In a complete binary tree every level, except possibly the last, is completely filled, and all nodes in the last level are as far left as possible. It can have between 1 and 2h nodes inclusive at the last level h.
Example:
Input: 1 / \ 2 3 / \ / 4 5 6 Output: 6
Method 1.
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
int countNodes(TreeNode* root) {
if (root == NULL)
return 0;
int depthLeft = 0, depthRight = 0;
TreeNode* curLeft = root, *curRight = root;
while (curLeft) {
depthLeft ++;
curLeft = curLeft->left;
}
while (curRight) {
depthRight ++;
curRight = curRight->right;
}
if (depthLeft == depthRight)
return pow(2, depthLeft) - 1;
return countNodes(root->left) + countNodes(root->right) + 1;
}
};
Method 2.
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
int countNodes(TreeNode* root) {
if (root == NULL)
return 0;
int res = 0;
queue<TreeNode*> que({root});
while (!que.empty()) {
TreeNode* cur = que.front();
res ++;
que.pop();
if (cur->left)
que.push(cur->left);
if (cur->right)
que.push(cur->right);
}
return res;
}
};