220503二叉树遍历-前序-递归

public class TreeNode {
    public int val;
    public TreeNode left;
    public TreeNode right;
    public int deep;
    public TreeNode(){}
    public TreeNode(int val) {this.val = val;}
    public TreeNode(int val, TreeNode left, TreeNode right) {
        this.val = val;
        this.left = left;
        this.right = right;
    }
}

public class BinaryTree {
    public static void main(String[] args) {
        TreeNode node7 = new TreeNode(7, null, null);
        TreeNode node6 = new TreeNode(6, null, null);
        TreeNode node5 = new TreeNode(5, node6, node7);
        TreeNode node4 = new TreeNode(4, null, null);
        TreeNode node3 = new TreeNode(3, null, null);
        TreeNode node2 = new TreeNode(2, node4, node5);
        TreeNode node1 = new TreeNode(1, node2, node3);

        preOrder(node1);
    }

        private static void preOrder(TreeNode node1) {
        if (null == node1) return;
        System.out.println(node1.val);// 前序：第一次称为栈顶元素时打印
        preOrder(node1.left);
        preOrder(node1.right);
    }
}