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

 1  public TreeNode pruneTree(TreeNode root) {
 2         dfs(root,null,-1);
 3         return root;
 4     }
 5 
 6     public void dfs(TreeNode cur, TreeNode fa, int left) {
 7         if (cur == null) return;
 8         if (check(cur)) {
 9             if (left == 1) fa.left = null;
10             else fa.right = null;
11         } else {
12             dfs(cur.left, cur, 1);
13             dfs(cur.right, cur, 0);
14         }
15         return;
16     }
17 
18     public boolean check(TreeNode node) {
19         if (node == null) return true;
20         if (node.val == 1) return false;
21         return check(node.left) && check(node.right);
22     }