先、中、后序遍历二叉树

/**
 * 先、中、后序遍历二叉树
 */
public class Code03 {

    public static class TreeNode{
        private Integer val;
        private TreeNode left;
        private TreeNode right;

        public TreeNode(Integer val) {
            this.val = val;
        }
    }

    public static void before(TreeNode node) {
        if (node == null){
            return;
        }
        System.out.println(node.val);
        before(node.left);
        before(node.right);
    }
    public static void in(TreeNode node){
        if (node == null){
            return;
        }
        in(node.left);
        System.out.println(node.val);
        in(node.right);
    }

    public static void after(TreeNode node){
        if (node == null){
            return;
        }
        after(node.left);
        after(node.right);
        System.out.println(node.val);
    }

    public static TreeNode generateTree(){
        TreeNode treeNode1 = new TreeNode(1);
        TreeNode treeNode2 = new TreeNode(2);
        TreeNode treeNode3 = new TreeNode(3);
        TreeNode treeNode4 = new TreeNode(4);
        TreeNode treeNode5 = new TreeNode(5);
        TreeNode treeNode6 = new TreeNode(6);
        TreeNode treeNode7 = new TreeNode(7);
        treeNode2.left = treeNode4;
        treeNode2.right = treeNode5;
        treeNode3.left = treeNode6;
        treeNode3.right = treeNode7;
        treeNode1.left = treeNode2;
        treeNode1.right = treeNode3;
        return treeNode1;
    }

    public static void main(String[] args) {
        TreeNode node = generateTree();
        before(node);
//        in(node);
//        after(node);
    }



}