606. Create a string from a binary tree (video explanation!!!)

13. （有视频）前序遍历二叉树 转成 字符串

原题链接

Preorder traversal of binary tree to string

public String tree2str(TreeNode root) {
    
    StringBuilder sb = new StringBuilder();
    tree2strChild(root,sb);
    return sb.toString();
}

private void tree2strChild(TreeNode t,StringBuilder sb) {
    
    if(t == null) return ;
    sb.append(t.val);

    if(t.left != null) {
    
        sb.append("(");
        tree2strChild(t.left,sb);
        sb.append(")");
    }else {
    
        if(t.right == null) {
    
            return;
        }else{
    
           sb.append("()");
        }
    }

    if(t.right == null) {
    
        return;
    }else{
    
        sb.append("(");
        tree2strChild(t.right,sb);
        sb.append(")");
    }
}