LeetCode-in-All
102. Binary Tree Level Order Traversal
Medium
Given the root of a binary tree, return the level order traversal of its nodes’ values. (i.e., from left to right, level by level).
Example 1:
Input: root = [3,9,20,null,null,15,7]
Output: [[3],[9,20],[15,7]]
Example 2:
Input: root = [1]
Output: [[1]]
Example 3:
Input: root = []
Output: []
Constraints:
- The number of nodes in the tree is in the range
[0, 2000]. -1000 <= Node.val <= 1000
Solution
/**
* Definition for a binary tree node.
* class TreeNode {
* public $val = null;
* public $left = null;
* public $right = null;
* function __construct($val = 0, $left = null, $right = null) {
* $this->val = $val;
* $this->left = $left;
* $this->right = $right;
* }
* }
*/
class Solution {
/**
* @param TreeNode $root
* @return Integer[][]
*/
function levelOrder($root) {
$result = array();
if ($root == null) {
return $result;
}
$queue = new \SplQueue();
$queue->enqueue($root);
$queue->enqueue(null);
$level = array();
while (!$queue->isEmpty()) {
$root = $queue->dequeue();
while (!$queue->isEmpty() && $root != null) {
array_push($level, $root->val);
if ($root->left != null) {
$queue->enqueue($root->left);
}
if ($root->right != null) {
$queue->enqueue($root->right);
}
$root = $queue->dequeue();
}
array_push($result, $level);
$level = array();
if (!$queue->isEmpty()) {
$queue->enqueue(null);
}
}
return $result;
}
}