二叉树的层次遍历

给出一棵二叉树，返回其节点值的层次遍历（逐层从左往右访问）

样例

给一棵二叉树 {3,9,20,#,#,15,7} ：



返回他的分层遍历结果：

[

    [3],

    [9,20],

    [15,7]

]

挑战

• 挑战1：只使用一个队列去实现它
• 挑战2：用DFS算法来做

标签

领英 脸书 二叉树遍历 队列 二叉树 宽度优先搜索优步

code

/**

 * Definition of TreeNode:

 * class TreeNode {

 * public:

 *     int val;

 *     TreeNode *left, *right;

 *     TreeNode(int val) {

 *         this->val = val;

 *         this->left = this->right = NULL;

 *     }

 * }

 */

class Solution {

    /**

     * @param root: The root of binary tree.

     * @return: Level order a list of lists of integer

     */

public:

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

        // write your code here

        vector<vector<int> > order;

        queue<TreeNode*> queue;

        int len;

        if(root == NULL) {

            return order;

        }

        queue.push(root);

        len = queue.size();

        while(!queue.empty()) {

            vector<int> base;

            len = queue.size();  

            while(len--) {

                TreeNode *tmp=queue.front();

                base.push_back(tmp->val);

                queue.pop();

                if(tmp->left)

                    queue.push(tmp->left);

                if(tmp->right)

                    queue.push(tmp->right);

            }

            order.push_back(base);

        }

        return order;

    }

};