LeetCode:Binary Tree Level Order Traversal II (按层遍历)

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]
]

/**
* 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<vector<int>> levelOrderBottom(TreeNode* root) {
vector<vector<int>> result;
traversal(root,1,result);
reverse(result.begin(),result.end()); //在原先的题的基础上reverse一下即可
return result;

}
//先序遍历 压入结果
void traversal(TreeNode *node,int level,vector<vector<int>> &result)
{
if(node==NULL) return;

if(level>result.size())
result.push_back(vector<int>());
result[level-1].push_back(node->val);
traversal(node->left,level+1,result);
traversal(node->right,level+1,result);

}
};