[LeetCode]Binary Tree Level Order Traversal II
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], ]
... 感觉很囧在,前一题的基础上 加了一句 reverse(ret.begin(),ret.end())
.好像编程之美上有这题,没注意看。
如果是每层的也要逆序的话,就把 left 和right 入队或入栈的顺序调换一下就行了
/**
* Definition for binary tree
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
vector<vector<int> > levelOrderBottom(TreeNode *root) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
vector<vector<int> > ret;
ret.clear();
if(root == NULL)
return ret;
queue<TreeNode*> S;
S.push(root);
S.push(NULL);
vector<int> tmp;
while(!S.empty()){
//travesal current level
TreeNode* p = S.front();
S.pop();
if(p!=NULL)
{
tmp.push_back(p->val);
if(p->left)
S.push(p->left);
if(p->right)
S.push(p->right);
}else{
if(!tmp.empty())
{
S.push(NULL);
ret.push_back(tmp);
tmp.clear();
}
}
}
reverse(ret.begin(),ret.end());
return ret;
}
};