# Trim-a-Binary-Search-Tree

Dec 05, 2017

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

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;
}

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