剑指 Offer 32 - I. 从上到下打印二叉树

剑指 Offer 32 - I. 从上到下打印二叉树

思路：

参考

代码：

/**
 * 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:
    vector<int> levelOrder(TreeNode* root) {
        if(!root) return {};
        queue<TreeNode*> q;
        q.push(root);
        vector<int> res;
        while(q.size()){
            int len = q.size();

            while(len--){
                auto t = q.front();
                q.pop();
                res.push_back(t->val);
                if(t->left) q.push(t->left);
                if(t->right) q.push(t->right);
            }
        }
        return res;
    }
};