[leetcode]144 Binary Tree Preorder traversal

Source: Internet
Author: User



/** * definition for binary tree * public class treenode {  *     int val; *     TreeNode left;  *     treenode right; *     treenode (int &NBSP;X)  { val = x; } * } */public class solution {     public list<integer> preordertraversal (TreeNode root)  {                 //  Solution a:        // return preordertraversal_ Recursion (Root);                 // solution b:        return preordertraversal_ iteration (root); &NBSP;&NBSP;&NBSP;&NBSP;}&NBSP;&Nbsp;  /////////////////////    // solution a: recursion     //    private list<integer> preordertraversal_recursion ( Treenode root)     {        list<integer > result = new ArrayList<> ();         Visit (Root, result);        return result;     }        private void visit (TreeNode node,  List<integer> result)     {        if   (Node == null)             return;                      result.add (node.val);         visit (Node.left, result);         visit (Node.right, result);    }         /////////////////////    // Solution A: Iteration     //    private list<integer> preordertraversal_iteration ( Treenode root)     {        list<integer > result = new ArrayList<> ();                 if  (root == null)              return result;                     Stack<TreeNode> stack  = new stack&lT;> ();         stack.push (Root);                 while  (!stack.empty ())          {             Treenode node = stack.pop ();                         result.add (Node.val);                          // Put right first             if  (node.right != null)                  stack.push (node.right);                             if  ( Node.left != null)                  stack.push (Node.left);        }                 return result;     }}

[leetcode]144 Binary Tree Preorder traversal

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