669 Trim a Binary Search Tree
669. Trim a Binary Search Tree
1. Question
Given a binary search tree and the lowest and highest boundaries asL
andR
, 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
2. Implementation
(1) Recursion
class Solution {
public TreeNode trimBST(TreeNode root, int L, int R) {
if (root == null) {
return null;
}
if (root.val > R) {
return trimBST(root.left, L, R);
}
if (root.val < L) {
return trimBST(root.right, L, R);
}
root.left = trimBST(root.left, L, R);
root.right = trimBST(root.right, L, R);
return root;
}
}
3. Time & Space Complexity
时间和空间复杂度都是O(n)
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