java Java二叉树遍历

Posted 2021-05-08

public List<TreeNode> preOrderTraversal(TreeNode root) {
    List<TreeNode> res = new ArrayList<>();
    if (root == null) {
        return res;
    }
    
    preOrderTraversal(root, res);
    
    return res;
}

private void preOrderTraversal(TreeNode root, List<TreeNode> res) {
    if (root == null) {
        return;
    }
    res.add(root);
    preOrderTraversal(root.left);
    preOrderTraversal(root.right);
}


private void inOrderTraversal(TreeNode root, List<TreeNode> res) {
    if (root == null) {
        return;
    }
    inOrderTraversal(root.left, res);
    res.add(root);
    inOrderTraversal(root.right, res);
}

private void postOrderTraversal(TreeNode root, List<TreeNode> res) {
    if (root == null) {
        return;
    }
    postOrderTraversal(root.left, res);
    postOrderTraversal(root.right, res);
    res.add(root);
}