Binary Tree Level Order Traversal II

问题：输出二叉树的每一行的结点，从叶子到根

/**

 * Definition for binary tree

 * struct TreeNode {

 *     int val;

 *     TreeNode *left;

 *     TreeNode *right;

 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}

 * };

 */

class Solution {

public:

    int dfs(TreeNode *root)

    {

        if(root==NULL) return 0;

        if(root->left==NULL && root->right==NULL) return 1;

        return max(dfs(root->left),dfs(root->right))+1;

    }

    void Ddfs(TreeNode *root,int t,vector<int> &vec,int step)

    {

        if(step==t) vec.push_back(root->val);

        if(root->left)  Ddfs(root->left,t,vec,step+1);

        if(root->right) Ddfs(root->right,t,vec,step+1);

    }

    vector<vector<int> > levelOrderBottom(TreeNode *root) {

        int height=dfs(root);

        vector<vector<int> > vec1;

        for(int i=height;i>=1;i--)

        {

            vector<int> vec2;

            Ddfs(root,i,vec2,1);

            vec1.push_back(vec2);

        }

        return vec1;

    }

};