669. Trim a Binary Search Tree

Medium

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]

Constraints:

• The number of nodes in the tree is in the range [1, 10^4].

• 0 <= Node.val <= 10^4

• The value of each node in the tree is unique.

• root is guaranteed to be a valid binary search tree.

• 0 <= low <= high <= 10^4

解題

Runtime: 6 ms, faster than 100%

Memory Usage: 6.4 MB, less than 100%

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func trimBST(root *TreeNode, low int, high int) *TreeNode {
    if root == nil { return nil }

    if root.Val < low {
        return trimBST(root.Right, low, high)
    } else if root.Val > high {
        return trimBST(root.Left, low, high)
    }

    return &TreeNode{ Val: root.Val, Left: trimBST(root.Left, low, high), Right: trimBST(root.Right, low, high) }
}