File tree Expand file tree Collapse file tree
solutions/144. Binary Tree Preorder Traversal Expand file tree Collapse file tree Original file line number Diff line number Diff line change 1+ /**
2+ * Definition for a binary tree node.
3+ * public class TreeNode {
4+ * int val;
5+ * TreeNode left;
6+ * TreeNode right;
7+ * TreeNode(int x) { val = x; }
8+ * }
9+ */
10+ public class Solution {
11+ public List <Integer > preorderTraversal (TreeNode root ) {
12+ List <Integer > res = new ArrayList <Integer >();
13+ if (root != null ){
14+ helper (root , res );
15+ }
16+ return res ;
17+ }
18+
19+ private void helper (TreeNode root , List <Integer > res ){
20+ if (root != null ){
21+ res .add (root .val );
22+ helper (root .left , res );
23+ helper (root .right , res );
24+ }
25+ }
26+ }
Original file line number Diff line number Diff line change 1+ /**
2+ * Definition for a binary tree node.
3+ * public class TreeNode {
4+ * int val;
5+ * TreeNode left;
6+ * TreeNode right;
7+ * TreeNode(int x) { val = x; }
8+ * }
9+ */
10+ public class Solution {
11+ public List <Integer > preorderTraversal (TreeNode root ) {
12+ List <Integer > res = new ArrayList <Integer >();
13+ Stack <TreeNode > stack = new Stack <TreeNode >();
14+
15+ if (root == null ){
16+ return res ;
17+ }
18+ stack .push (root );
19+ while (!stack .isEmpty ()){
20+ TreeNode node = stack .pop ();
21+ res .add (node .val );
22+
23+ //×¢ÒâÏÈpushÓÒ½Úµã
24+ if (node .right != null ) stack .push (node .right );
25+ if (node .left != null ) stack .push (node .left );
26+ }
27+ return res ;
28+ }
29+ }
You can’t perform that action at this time.
0 commit comments