题解 | #从上往下打印二叉树#

/*
struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
    TreeNode(int x) :
            val(x), left(NULL), right(NULL) {
    }
};*/
#include <cstddef>
class Solution {
  public:
    vector<int> PrintFromTopToBottom(TreeNode* root) {
        vector<int> v;
        if (root == nullptr) {
            return v;
        }
        //用队列存储每一个结点，出队时若当前结点有孩子则将孩子入队
        queue<TreeNode*> q;
        q.push(root);
        while (!q.empty()) {
            v.push_back(q.front()->val);
            if (q.front()->left != nullptr) {
                q.push(q.front()->left);
            }
            if (q.front()->right != nullptr) {
                q.push(q.front()->right);
            }
            q.pop();
        }
        return v;
    }
};