Pre-sequence traversal (recursive, non-recursive)

Recursion:

1  PackageThe sword refers to an offer . Pre-sequence traversal;2 3 Importjava.util.ArrayList;4 5 /**6 * Created by Nick on 2018/10/6.7  */8  Public classSolution {9Arraylist<integer> res=NewArraylist<integer>();Ten      Public voidPrenode (TreeNode root) { One         if(root==NULL) A             return; - Res.add (root.val); - Prenode (root.left); the Prenode (root.right); -     } -      - } + classTreeNode { -     intval = 0; +TreeNode left =NULL; ATreeNode right =NULL; at  -      PublicTreeNode (intval) { -          This. val =Val; -  -     } -}

Non-recursive:

1  PackageThe sword refers to an offer . Pre-sequence traversal;2 3 Importjava.util.ArrayList;4 ImportJava.util.Stack;5 6 /**7 * Created by Nick on 2018/10/6.8  */9  Public classSolution1 {TenArraylist<integer> res=NewArraylist<integer>(); One      PublicArraylist<integer>Prenode (TreeNode root) { AStack<treenode> temp=NewStack<treenode>(); -         if(root==NULL) -             returnRes; the Temp.push (root); -          while(!Temp.isempty ()) { -TreeNode t=Temp.pop (); - Res.add (t.val); +             if(t.right!=NULL) - Temp.push (root.right); +             if(t.left!=NULL) A Temp.push (root.left); at  -         } -         returnRes; -     } -  -      Public Static voidMain (string[] args) { inTreeNode root=NewTreeNode (1); -root.left=NewTreeNode (2); toroot.right=NewTreeNode (3); +  -System.out.println (NewSolution1 (). Prenode (root)); the     } *}

Pre-sequence traversal (recursive, non-recursive)