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],] 先查看有几层，然后填进去。

/** * 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
     
      
        > re;    int levv;    vector
       
        
          > levelOrderBottom(TreeNode *root) {        if(root == NULL)return re;        levv = level(root);        for(int i = 0 ; i < levv ;i++)        {            vector
         
           vec;            re.push_back(vec);        }        bottom(root,1);                return re;    }    void bottom(TreeNode * root ,int lev)    {        if(root == NULL)return;        re[levv - lev].push_back(root->val);        bottom(root->left,lev+1);        bottom(root->right,lev+1);    }    int level(TreeNode *root)    {        if(root->left == NULL && root ->right == NULL)return 1;        else if(root->left == NULL) return level(root->right)+1;        else if(root->right == NULL) return level(root->left)+1;        else        return max(level(root->left),level(root->right))+1;    }};