DFS Traversal Binary Tree without Recurrsion

Introduction

DFS is the basic traversal solution of the binary tree. Normally it is easy to use the recurrsion to solve the DFS. However, interative also could work for DFS

Solution

PostOrder

	public List<Integer> postorderTraversal(TreeNode root) {
		List<Integer> list = new ArrayList<>();
		Stack<TreeNode> s1 = new Stack<>();
		if(root == null)
			return list;
		s1.push(root);
		while(!s1.isEmpty() && root != null) {
			TreeNode temp1 = s1.pop();
			if(temp1.left != null)
				s1.push(temp1.left);
			if(temp1.right != null)
				s1.push(temp1.right);
			
			list.add(0, temp1.val);
		}
		
		return list;
	}