669. Trim a Binary Search Tree
这个比较简单
https://leetcode.com/problems/trim-a-binary-search-tree/discuss/107000/Java-solution-6-liner
1 //Old 2 class Solution { 3 TreeNode dummy = new TreeNode(Integer.MAX_VALUE); 4 public TreeNode trimBST(TreeNode root, int L, int R) { 5 if(root == null) return null; 6 preorder(root, L, R); 7 return dummy.left; 8 9 } 10 11 public void preorder(TreeNode root, int L, int R){ 12 if(root == null) return; 13 if(root.val >= L && root.val <= R){ 14 build(dummy, root.val); 15 } 16 preorder(root.left, L, R); 17 preorder(root.right, L, R); 18 } 19 20 public void build(TreeNode root, int val){ 21 if(root.val < val){ 22 if(root.right == null){ 23 root.right = new TreeNode(val); 24 }else{ 25 build(root.right, val); 26 } 27 28 }else{ 29 if(root.left == null){ 30 root.left = new TreeNode(val); 31 }else{ 32 build(root.left, val); 33 } 34 35 } 36 37 } 38 }