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Copy pathbinaryTreeLevelOrderTraversal.java
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39 lines (37 loc) · 1004 Bytes
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/*
Given a binary tree, return the level order traversal of its nodes' values.
(ie, from left to right, level by level).
For example:
Given binary tree [3,9,20,null,null,15,7],
3
/ \
9 20
/ \
15 7
return its level order traversal as:
[
[3],
[9,20],
[15,7]
]
*/
class Solution {
public List<List<Integer>> levelOrder(TreeNode root) {
List<List<Integer>> res = new ArrayList<List<Integer>>();
if (root == null) return res;
Queue<TreeNode> queue = new LinkedList<>();
queue.offer(root);
while(!queue.isEmpty()) {
int size = queue.size();
List<Integer> list = new ArrayList<>();
for (int i = 0; i < size; i++) {
TreeNode node = queue.poll();
list.add(node.val);
if(node.left != null) queue.offer(node.left);
if (node.right != null) queue.offer(node.right);
}
res.add(list);
}
return res;
}
}