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.
Example 1:
Input:
1
/ \
0 2
L = 1
R = 2
Output:
1
\
2
Example 2:
Input:
3
/ \
0 4
\
2
/
1
L = 1
R = 3
Output:
3
/
2
/
1
思路:
1.如果root在[L,R]范围内,返回root,并处理它的左子树和右子树.
2.若root的val < L,则其左子树必小于L,因此root和其左子树不用再管,处理右子树.
3.若root的val > R,思路类比于2.
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
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;
}
};
