leetcode 98. 验证二叉搜索树 【时间击败73.33%】【内存击败36.17%】

 1   boolean ans = true;
 2 
 3     public boolean isValidBST(TreeNode root) {
 4         if (root == null) return true;
 5         dfs(root);
 6         return ans;
 7     }
 8 
 9     long[] dfs(TreeNode r) {
10         long[] T = new long[]{Long.MAX_VALUE, Long.MIN_VALUE};
11         if (ans == false) return T;
12         if (r == null) return T;
13         long[] left = dfs(r.left);
14         long[] right = dfs(r.right);
15         if (!(left[1] < r.val && r.val < right[0])) {
16             ans = false;
17             return T;
18         }
19         left[0]=Math.min(left[0], r.val);
20         left[1]=Math.max(right[1], r.val);
21         return left;
22     }