recursion programming
1 public class Solution { 2 public ArrayList<Integer> postorderTraversal(TreeNode root) { 3 // IMPORTANT: Please reset any member data you declared, as 4 // the same Solution instance will be reused for each test case. 5 ArrayList<Integer> result = new ArrayList<Integer>(); 6 traversal(result, root); 7 return result; 8 } 9 private void traversal(ArrayList<Integer> result, TreeNode node) 10 { 11 if(node == null) 12 return; 13 traversal(result, node.left); 14 traversal(result, node.right); 15 result.add(node.val); 16 } 17 }
1 public ArrayList<Integer> postorderTraversal(TreeNode root) { 2 // IMPORTANT: Please reset any member data you declared, as 3 // the same Solution instance will be reused for each test case. 4 ArrayList<Integer> result = new ArrayList<Integer>(); 5 if(root == null){ 6 return result; 7 } 8 9 Stack<TreeNode> stack = new Stack<TreeNode>(); 10 TreeNode cur = null, pre = null; 11 stack.push(root); 12 13 while(!stack.empty()){ 14 cur = stack.peek(); 15 if((cur.left == null && cur.right == null) || 16 ((pre != null) && (cur.left == pre || cur.right == pre))){ 17 result.add(cur.val); 18 pre = cur; 19 stack.pop(); 20 } else { 21 if(cur.right != null){ 22 stack.push(cur.right); 23 } 24 if(cur.left != null){ 25 stack.push(cur.left); 26 } 27 } 28 29 } 30 31 return result; 32 }