669. Trim a Binary Search Tree

Given the root of a binary search tree and the lowest and highest boundaries as low and high, trim the tree so that all its elements lies in [low, high]. Trimming the tree should not change the relative structure of the elements that will remain in the tree (i.e., any node's descendant should remain a descendant). It can be proven that there is a unique answer.

Return the root of the trimmed binary search tree. Note that the root may change depending on the given bounds.

 

Example 1:

Input: root = [1,0,2], low = 1, high = 2
Output: [1,null,2]

Example 2:

Input: root = [3,0,4,null,2,null,null,1], low = 1, high = 3
Output: [3,2,null,1]

Example 3:

Input: root = [1], low = 1, high = 2
Output: [1]

Example 4:

Input: root = [1,null,2], low = 1, high = 3
Output: [1,null,2]

Example 5:

Input: root = [1,null,2], low = 2, high = 4
Output: [2]

 

Constraints:

  • The number of nodes in the tree in the range [1, 104].
  • 0 <= Node.val <= 104
  • The value of each node in the tree is unique.
  • root is guaranteed to be a valid binary search tree.
  • 0 <= low <= high <= 104

Rust Solution

struct Solution;
use rustgym_util::*;

impl Solution {
    fn trim_bst(root: TreeLink, l: i32, r: i32) -> TreeLink {
        if let Some(node) = root.clone() {
            let mut node = node.borrow_mut();
            let left = node.left.take();
            let right = node.right.take();
            if node.val > r {
                return Self::trim_bst(left, l, r);
            }
            if node.val < l {
                return Self::trim_bst(right, l, r);
            }
            node.left = Self::trim_bst(left, l, r);
            node.right = Self::trim_bst(right, l, r);
            root
        } else {
            None
        }
    }
}

#[test]
fn test() {
    let root = tree!(1, tree!(0), tree!(2));
    let res = tree!(1, None, tree!(2));
    assert_eq!(Solution::trim_bst(root, 1, 2), res);
    let root = tree!(3, tree!(0, None, tree!(2, tree!(1), None)), tree!(4));
    let res = tree!(3, tree!(2, tree!(1), None), None);
    assert_eq!(Solution::trim_bst(root, 1, 3), res);
}

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