题目
Given a binary search tree and the lowest and highest boundaries as L and R, trim the tree so that all its elements lies in [L, R] (R >= L). You might need to change the root of the tree, so the result should return the new root of the trimmed binary search tree.
答案
Think recursively!
public TreeNode trimBST(TreeNode root, int L, int R) {
if(root == null) return null;
if(root.val < L) return trimBST(root.right, L, R);
if(root.val > R) return trimBST(root.left, L, R);
root.left = trimBST(root.left, L, R);
root.right = trimBST(root.right, L, R);
return root;
}
