3. Find Level Order Traversal of a Binary Tree.
Oct 19, 2020
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]
]
Solution
class Solution {
public List<List<Integer>> levelOrder(TreeNode root) {
List<List<Integer>> sol = new ArrayList<>();
if (root == null) {
return sol;
}
Queue<TreeNode> q = new LinkedList<>();
q.offer(root);
while(!q.isEmpty()){
int levelSize = q.size();
List<Integer> level = new ArrayList<>();
while(levelSize → 0){
TreeNode t = q.poll();
level.add(t.val);
if(t.left != null){
q.offer(t.left);
}
if(t.right != null) {
q.offer(t.right);
}
}
sol.add(level);
}
return sol;
}
}