2023.7.3

        用层序遍历遍历一遍二叉树，然后遍历的每个节点都进行一次计数，直接上代码：

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