java分别按照二叉树先序，中序和后序打印所有的节点。

//用递归，先计算树的结点数，然后在用递归来分别遍历，存到数组中就好了
import java.util.*;

/*

• public class TreeNode {
• int val = 0;
• TreeNode left = null;
• TreeNode right = null;
• }
• /

public class Solution {
int n;
int[][] order;//restore the 3 kinds of order;
/**
*
* @param root TreeNode类 the root of binary tree
* @return int整型二维数组
*/
public int[][] threeOrders (TreeNode root) {
// write code here
n = countTree(root);
order=new int[3][n];
preOrder(root);
midOrder(root);
lastOrder(root);
return order;
}

//count The tree node_number
public int countTree(TreeNode root){
    if(root==null){
        return n; 
    }else{
        n++;
        countTree(root.left);
        countTree(root.right);
    }
    return n;
}
int pre1 = -1;
//pre_order
public void preOrder(TreeNode root){
    if(root==null){
        return;
    }else{
        order[0][++pre1]=root.val;
        preOrder(root.left);
        preOrder(root.right);
    }    
}

int mid1 = -1;
//pre_order
public void midOrder(TreeNode root){
    if(root==null){
        return;
    }else{
        midOrder(root.left);
        order[1][++mid1]=root.val;
        midOrder(root.right);
    }    
}


int last1 = -1;
//pre_order
public void lastOrder(TreeNode root){
    if(root==null){
        return;
    }else{
        lastOrder(root.left);
        lastOrder(root.right);
        order[2][++last1]=root.val;
    }    
}

}