二叉树三种遍历的实现(递归)

• 前序递归遍历算法：访问根结点-->递归遍历根结点的左子树-->递归遍历根结点的右子树
• 中序递归遍历算法：递归遍历根结点的左子树-->访问根结点-->递归遍历根结点的右子树
• 后序递归遍历算法：递归遍历根结点的左子树-->递归遍历根结点的右子树-->访问根结点

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    //前序遍历
    public void preOrder(TreeNode root){
        if(null!=root){
            System.out.print(root.val + "\t");
            preOrder(root.left);
            preOrder(root.right);
        }
    }
    //中序遍历
    public void midOrder(TreeNode root){
        if(root != null){
            midOrder(root.left);
            System.out.print(root.val + "\t");
            midOrder(root.right);
        }
    }
    //后序遍历
    public void postOrder(TreeNode root){
        if(root!=null){
            postOrder(root.left);
            postOrder(root.right);
            System.out.print(root.val + "\t");
        }
    }
}