劍指offer-把二叉樹打印成多行（python和c++）

題目描述

從上到下按層打印二叉樹，同一層結點從左至右輸出。每一層輸出一行。

思路：
每一次維護兩個列表，循環一層先把該層的根節點添加進一個列表，再判斷該層節點的左右子節點是否存在，存在就把left和right的節點的都添加進去，依次遍歷添加進最後的res。

python

# -*- coding:utf-8 -*-
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
class Solution:
    # 返回二維列表[[1,2],[4,5]]
    def Print(self, pRoot):
        # write code here
        if not pRoot:
            return []
        result = []
        nodeStack = [pRoot]
        while nodeStack:
            res = []
            nextStack = []
            for i in nodeStack:
                res.append(i.val)
                if i.left:
                    nextStack.append(i.left)
                if i.right:
                    nextStack.append(i.right)
            nodeStack = nextStack
            result.append(res)
        return result
    

c++

class Solution {
public:
        vector<vector<int> > Print(TreeNode* pRoot) {
            vector<vector<int> > vec;
            if(pRoot == NULL) return vec;
 
            queue<TreeNode*> q;
            q.push(pRoot);
 
            while(!q.empty())
            {
                int lo = 0, hi = q.size();
                vector<int> c;
                while(lo++ < hi)
                {
                    TreeNode *t = q.front();
                    q.pop();
                    c.push_back(t->val);
                    if(t->left) q.push(t->left);
                    if(t->right) q.push(t->right);
                }
                vec.push_back(c);
            }
            return vec;
        }
};