LintCode-69.二叉树的层次遍历

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;
    }
};