LeetCode107—Binary Tree Level Order Traversal II

LeetCode107—Binary Tree Level Order Traversal II

根据前/后序+中序遍历曾经考试常考，然而代码没写过，真是十分无奈。。等过两天学习了再来写

这题是二叉树层序遍历。

原题

Given a binary tree, return the bottom-up level order traversal of its nodes’ values. (ie, from left to right, level by level from leaf to root).

For example:

Given binary tree {3,9,20,#,#,15,7},

　　　　3

　　　/　　\

　　9　　　20

　　　　　/　　\

　　　　15　　　7

return its bottom-up level order traversal as:

[

[15,7],

[9,20],

[3]

]

分析

层序遍历啊，然后把容器逆置，最简单直观的办法，至于还有没有更好的方法，等知道再写吧…

代码

class Solution {
private:
void help(vector<vector<int>>&result,TreeNode * root)
{
if(root == NULL)
return;
vector<TreeNode*> q;
vector<int>tmp;
int front = 0;
int rear =1;
q.push_back(root);
while(front < q.size())
{
rear=q.size();
while(front < rear)
{
tmp.push_back(q[front]->val);
if(q[front]->left !=NULL)
q.push_back(q[front]->left);
if(q[front]->right !=NULL)
q.push_back(q[front]->right);
++front;
}
result.push_back(tmp);
tmp.clear();
}
}
public:
vector<vector<int>> levelOrderBottom(TreeNode* root) {
vector<vector<int>>result;
help(result,root);
vector<vector<int>>inverse(result.rbegin(),result.rend());
return inverse;
}
};