题目

迭代做法

cpp
class Solution {
public:
    int countNodes(TreeNode* root) {
  if(!root) return 0;
  
  queue<TreeNode*> q;
  q.push(root);
  
  int count = 0;
  while(!q.empty()) {
    TreeNode* node = q.front();
    q.pop();
    
    if(node->left) {
      q.push(node->left); 
    }
    
    if(node->right) {
      q.push(node->right);
    }
    
    count++;
  }
  
  return count;
}
};

递归做法

cpp
class Solution {
public:
    int countNodes(TreeNode* root) {
  if(!root) return 0;
  
  return 1 + countNodes(root->left) + countNodes(root->right);
}
};