import java.util.Stack;

public class test_04_23 {
    //二叉树的三种遍历
    static class TreeNode{
        int data;
        TreeNode left;
        TreeNode right;
        public TreeNode(int data){
            this.data = data;
        }
    }
    //先序遍历
    public static void test1(TreeNode root){
        Stack<TreeNode> stack = new Stack<>();
        stack.push(root);
        while (!stack.isEmpty()){
            TreeNode node = stack.pop();
            System.out.println(node.data);
            if (node.right!=null){
                stack.push(node.right);
            }
            if (node.left!=null){
                stack.push(node.left);
            }
        }
    }
    //中序遍历
    public static void test2(TreeNode root){
        Stack<TreeNode> stack = new Stack<>();
        TreeNode p = root;
        while (p!=null||!stack.isEmpty()){
            if (p!=null){
                stack.push(p);
                p=p.left;
            }else{
                TreeNode node = stack.pop();
                System.out.println(node.data);
                if (node.right!=null){
                    p=node.right;
                }
            }
        }
    }
    //后序遍历
    public static void test3(TreeNode root){
        Stack<TreeNode> stack = new Stack<>();
        TreeNode p = root;
        TreeNode r = null;
        while (p!=null||!stack.isEmpty()){
            if (p!=null){
                stack.push(p);
                p=p.left;
            }else{
                TreeNode pNode = stack.peek();
                if (pNode.right!=null&&pNode.right!=r){
                    p=pNode.right;
                }else{
                    TreeNode node = stack.pop();
                    System.out.println(node.data);
                    r = pNode;
                }
            }
        }
    }
    //    1
    //  2   3
    // 4 5 6 7
    public static void main(String[] args) {
        TreeNode root = new TreeNode(1);
        root.left=new TreeNode(2);
        root.right=new TreeNode(3);
        root.left.left=new TreeNode(4);
        root.left.right=new TreeNode(5);
        root.right.left=new TreeNode(6);
        root.right.right=new TreeNode(7);
        test3(root);
    }
}