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). http://www.leetcode.com/onlinejudge

leetcode_binary_tree_level_order_traversal2.cpp

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    void dfs(vector< vector<int> >& ret, int maxDepth, int curDepth, TreeNode* node) {
        if (node == NULL) {
            return;
        }
        dfs(ret, maxDepth, curDepth + 1, node->left);
        dfs(ret, maxDepth, curDepth + 1, node->right);
        ret[maxDepth - 1 - curDepth].push_back(node->val);
    }
    
    int getDepth(TreeNode* root) {
        if (root == NULL) {
            return 0;
        }
        else {
            return 1 + max(getDepth(root->left), getDepth(root->right));
        }
    }

    vector<vector<int> > levelOrderBottom(TreeNode *root) {
        int maxDepth = getDepth(root);
        vector< vector<int> > ret(maxDepth);
        dfs(ret, maxDepth, 0, root);
        return ret;
    }
};