lintcode-dfs实现二叉树的层序遍历

class Solution {
    /**
     * @param root: The root of binary tree.
     * @return: Level order a list of lists of integer
     */
    struct node{
        TreeNode* tn;
        int cnt;
        node(TreeNode* tn, int cnt){
                this->tn = tn;
                this->cnt = cnt;
        }
    };

public:
    void dfs(vector<vector<int>> &ans, queue<node*> &que){
            if(que.empty()) return ;
            node* now = que.front();
            que.pop();

            if(now->tn->left) que.push(new node(now->tn->left, now->cnt + 1));
            if(now->tn->right) que.push(new node(now->tn->right, now->cnt + 1));
            
            if((int)ans.size() - 1 < now->cnt){
                vector<int> v(1,now->tn->val);
                ans.push_back(v);

            } else {
                ans[now->cnt].push_back(now->tn->val);
            }

            dfs(ans, que);

    }
    vector<vector<int>> levelOrder(TreeNode *root) {
        // write your code here
        vector<vector<int>> ans;
        if(root == NULL) return ans;
        queue<node*> que;
        que.push(new node(root,0));
        dfs(ans, que);
        return ans;
    }
};