代码随想录训练营第十四天 ｜ 二叉树

class Solution {
    public List<Integer> preorderTraversal(TreeNode root) {
        List<Integer> res = new ArrayList<>();
        preoder(root,res);
        return res;
    }
    public void preoder(TreeNode root, List<Integer> res){
        if(root == null){
            return;
        }
        res.add(root.val);
        preoder(root.left, res);
        preoder(root.right, res);
        
    }
}

class Solution {
    public List<Integer> postorderTraversal(TreeNode root) {
        List<Integer> res = new ArrayList<>();
        postOrder(root,res);
        return res;
    }
    public void postOrder(TreeNode root, List<Integer> res){
        if (root == null){
            return;
        }
        postOrder(root.left, res);
        postOrder(root.right, res);
        res.add(root.val);
        

    }
}

class Solution {
    public List<Integer> inorderTraversal(TreeNode root) {
        List<Integer> res = new ArrayList<>();
        inorder(root, res);
        return res;
    }
    public void inorder(TreeNode root, List<Integer> res){
        if(root == null){
            return ;
        }
        inorder(root.left, res);
        res.add(root.val);
        inorder(root.right, res);
    }
}