第69天。
今天的题目是Trim a Binary Search Tree:
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
一开始没看到时二叉排序树，然后写的就有点复杂了：
TreeNode* trimBST(TreeNode* root, int L, int R) {
if (!root) return nullptr;
root->left = trimBST(root->left,L,R);
root->right = trimBST(root->right,L,R);
if (root->val >= L && root->val <= R) return root;
else if (root->left != nullptr && root->right != nullptr) {
auto p = root->left;
while(p->left) p = p->left;
p->left = root->right;
return root->left;
}
return (root->left)?root->left:root->right;
}
TreeNode* trimBST(TreeNode* root, int L, int R) {
if (root == nullptr) return nullptr;
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;
}