Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to right, level by level). http://www.leetcode.com/onlinejudge

leetcode_binary_tree_level_order_traversal.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 bfs(vector< vector<int> >& ret, int& maxDepth, int curDepth, TreeNode* node) {
        if (node == NULL) {
            return;
        }
        if (curDepth > maxDepth) {
            ret.resize(curDepth + 1);
            maxDepth = curDepth;
        }
        ret[curDepth].push_back(node->val);
        bfs(ret, maxDepth, curDepth + 1, node->left);
        bfs(ret, maxDepth, curDepth + 1, node->right);
    }

    vector<vector<int> > levelOrder(TreeNode *root) {
        vector< vector<int> > ret;
        int maxDepth = -1;
        bfs(ret, maxDepth, 0, root);
        return ret;
    }
};