leetcode 814. 二叉树剪枝 【时间击败100.00%】【 内存击败84.62%】

 public TreeNode pruneTree(TreeNode root) {
        dfs(root,null,-1);
        return root;
    }

    public void dfs(TreeNode cur, TreeNode fa, int left) {
        if (cur == null) return;
        if (check(cur)) {
            if (left == 1) fa.left = null;
            else fa.right = null;
        } else {
            dfs(cur.left, cur, 1);
            dfs(cur.right, cur, 0);
        }
        return;
    }

    public boolean check(TreeNode node) {
        if (node == null) return true;
        if (node.val == 1) return false;
        return check(node.left) && check(node.right);
    }