Tree - Level Order Traversal

levelOrderTraversal.java

class GfG
{
    void levelOrder(Node node) 
    {
        int h = height(node);
        for(int i=0;i<h;i++){
            lev(node,i);
        }
    }
    
    void lev(Node node,int level){
        if(node==null) return;
        
        if(level==0) System.out.print(node.data+" ");
        else {
            lev(node.left,level-1);
            lev(node.right,level-1);
        }
    }
    
    int height(Node node){
        if(node==null) return 0;
        else{
            int lh = height(node.left);
            int rh = height(node.right);
            
            return lh>rh ? lh+1:rh+1;
            
        }
    }
}






Level Order traversal 2nd type, without recursion

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public List<List<Integer>> levelOrder(TreeNode root) {
        List<List<Integer>> list = new ArrayList<>();
        level(list,0,root);
        return list;
    }
    
    public void level(List<List<Integer>> ans, int level, TreeNode root){
        if(root==null) return;
        
        if(ans.size()==level){
            List<Integer> newL = new ArrayList<>();
            ans.add(newL);
        }
        
        List<Integer> list = ans.get(level);
        list.add(root.val);
        level(ans,level+1,root.left);
        level(ans,level+1,root.right);
    }
}