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;
}
};