有一棵二叉树，请设计一个算法，按照层次打印这棵二叉树。

给定二叉树的根结点root，请返回打印结果，结果按照每一层一个数组进行储存，所有数组的顺序按照层数从上往下，且每一层的数组内元素按照从左往右排列。保证结点数小于等于500。

C++实现

/*
struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
    TreeNode(int x) :
            val(x), left(NULL), right(NULL) {
    }
};*/
 
class TreePrinter {
public:
    vector< vector<int> > printTree(TreeNode* root) {
        // write code here
        vector< vector<int> >  results;
        queue<TreeNode *> myq;
        myq.push(root);
        struct TreeNode * temp;
        struct TreeNode * nlast = root;
        struct TreeNode* last  = root;
        vector<int> temp_row;
        while (!myq.empty()) {
            temp = myq.front();
            if (temp->left) {
                myq.push(temp->left);
                nlast = temp->left;
            }
            if (temp->right) {
                myq.push(temp->right);
                nlast = temp->right;
            }
            temp_row.push_back(temp->val);
            if (temp==last) {
                results.push_back(temp_row);
                temp_row.clear();
                last = nlast;
            }
            myq.pop();
        }
        return results;
 
    }
};

Python 实现

# -*- coding:utf-8 -*-

# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
class TreePrinter:
    def printTree(self, root):
        # write code here
        q, row , results = [],[],[]
        last, nlast = root, root
        q.append(root);
        while q:
            tmp = q.pop(0)
            if tmp.left:
                q.append(tmp.left)
                nlast = tmp.left
            if tmp.right:
                q.append(tmp.right)
                nlast = tmp.right
            row.append(tmp.val)
            if last == tmp:
                last = nlast
                results.append(row)
                row = []
        return results