Question:
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,#,#,15,7},
3
/ 9 20
/ 15 7
return its level order traversal as:
[ [3], [9,20], [15,7] ]
confused what "{1,#,2,3}" means?
/**
* Definition for binary tree
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public ArrayList<ArrayList<Integer>> levelOrder(TreeNode root) {
ArrayList<ArrayList<Integer>> results = new ArrayList<ArrayList<Integer>>();
traverse(root,1,results);
return results;
}
private void traverse(TreeNode root, int level,
ArrayList<ArrayList<Integer>> results) {
if(root==null) return;
if(level>results.size())
results.add(new ArrayList<Integer>());
results.get(level-1).add(root.val);
traverse(root.left, level+1, results);
traverse(root.right, level+1, results);
}
}