Leetcode 二叉树中序遍历 前序遍历 后序遍历（递归）

中序遍历：

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public List<Integer> inorderTraversal(TreeNode root) {
        List<Integer> tree=new ArrayList<>(); //建立一个动态数组
        inorder(root,tree); //调用递归函数，实参
        return tree;

    }

    public void inorder(TreeNode root, List<Integer> tree){
        // TreeNode root,List<Interger> tree都是传入的形参
        if(root==null){
            return;
        }
        inorder(root.left,tree);  //遍历左子树
        tree.add(root.val); //将当前值加入动态数组中
        inorder(root.right,tree); //遍历右子树

    }
    
}

前序遍历

class Solution {
    public List<Integer> inorderTraversal(TreeNode root) {
            List<Integer> tree =new ArrayList<Integer>();
            PreOrder(root,tree);
            return tree;

    }

    public void PreOrder(TreeNode root, List<Integer> tree){
        if(tree==null){
        return;}
        tree.add(root.val);
        PreOrder(root.left,tree);
        PreOrder(root.right,tree);
    


    }





}

}

后序遍历

class Solution {
    public List<Integer> inorderTraversal(TreeNode root) {
            List<Integer> tree =new ArrayList<Integer>();
            PostOrder(root,tree);
            return tree;

    }

    public void PostOrder(TreeNode root, List<Integer> tree){
        if(tree==null){
        return;}
        PostOrder(root.left,tree);
        PostOrder(root.right,tree);
        tree.add(root.val);
    


    }





}

}