Summary_bt

08 Nov 2021 in Algorithms

• Inorder

  class Solution {
      List<Integer> inorder = new ArrayList<>();
        
      public List<Integer> inorderTraversal(TreeNode root) {
          helper(root);
          return inorder;
      }
        
      public void helper(TreeNode tn){
          if (root != null) {
              helper(tn.left);            
              inorder.add(tn.val);
              helper(tn.right);    
          }
      }
  }
  

• Preorder

  class Solution {
      List<Integer> preorder = new ArrayList<>();
        
      public List<Integer> preorderTraversal(TreeNode root) {
          helper(root);
          return preorder;
      }
        
      public void helper(TreeNode tn){
          if(tn!=null){
              preorder.add(tn.val);
              helper(tn.left);
              helper(tn.right);
          }
      }   
  }
  

• Postorder

  ```java class Solution { List postorder = new ArrayList<>();

  public List<Integer> postorderTraversal(TreeNode root) {
      helper(root);
      return postorder;
  }
    
  public void helper(TreeNode tn){
      if(tn!=null){
          helper(tn.left);
          helper(tn.right);
          postorder.add(tn.val);
      }
  } }