Create 0145-binary-tree-postorder-traversal

Adding the Java solutions for the Postorder traversal

java/0145-binary-tree-postorder-traversal

@@ -0,0 +1,46 @@
+class Solution {
+ // Iterative
+ public List<Integer> postorderTraversal(TreeNode root) {
+ Stack<TreeNode> stack = new Stack<>();
+ stack.add(root);
+ Stack<Boolean> visit = new Stack<>();
+ visit.add(false);
+
+ List<Integer> res = new ArrayList<>();
+
+ while(!stack.isEmpty()){
+ TreeNode curr=stack.pop();
+ boolean v = visit.pop();
+ if(curr != null){
+ if(v != false){
+ res.add(curr.val);
+ }else{
+ stack.add(curr);
+ visit.add(true);
+ stack.add(curr.right);
+ visit.add(false);
+ stack.add(curr.left);
+ visit.add(false);
+ }
+ }
+ }
+ return res;
+ }
+}
+
+class Solution {
+ // Recursive
+ public void postorder(TreeNode root, List<Integer> res){
+ if(root == null) return;
+
+ postorder(root.left, res);
+ postorder(root.right, res);
+ res.add(root.val);
+ }
+ public List<Integer> postorderTraversal(TreeNode root) {
+ List<Integer> res = new ArrayList<>();
+
+ postorder(root, res);
+ return res;
+ }
+}