g1901_2000.s1932_merge_bsts_to_create_single_bst

Class Solution

java.lang.Object

g1901_2000.s1932_merge_bsts_to_create_single_bst.Solution

public class Solution
extends Object

1932 - Merge BSTs to Create Single BST.

Hard

You are given n BST (binary search tree) root nodes for n separate BSTs stored in an array trees ( 0-indexed ). Each BST in trees has at most 3 nodes , and no two roots have the same value. In one operation, you can:

• Select two distinct indices i and j such that the value stored at one of the leaves of trees[i] is equal to the root value of trees[j].
• Replace the leaf node in trees[i] with trees[j].
• Remove trees[j] from trees.

Return the root of the resulting BST if it is possible to form a valid BST after performing n - 1 operations, or null if it is impossible to create a valid BST.

A BST (binary search tree) is a binary tree where each node satisfies the following property:

• Every node in the node’s left subtree has a value strictly less than the node’s value.
• Every node in the node’s right subtree has a value strictly greater than the node’s value.

A leaf is a node that has no children.

Example 1:

Input: trees = [[2,1],[3,2,5],[5,4]]

Output: [3,2,5,1,null,4]

Explanation: In the first operation, pick i=1 and j=0, and merge trees[0] into trees[1]. Delete trees[0], so trees = [[3,2,5,1],[5,4]]. In the second operation, pick i=0 and j=1, and merge trees[1] into trees[0]. Delete trees[1], so trees = [[3,2,5,1,null,4]]. The resulting tree, shown above, is a valid BST, so return its root.

Example 2:

Input: trees = [[5,3,8],[3,2,6]]

Output: []

Explanation: Pick i=0 and j=1 and merge trees[1] into trees[0]. Delete trees[1], so trees = [[5,3,8,2,6]]. The resulting tree is shown above. This is the only valid operation that can be performed, but the resulting tree is not a valid BST, so return null.

Example 3:

Input: trees = [[5,4],[3]]

Output: []

Explanation: It is impossible to perform any operations.

Constraints:

• n == trees.length
• 1 <= n <= 5 * 104
• The number of nodes in each tree is in the range [1, 3].
• Each node in the input may have children but no grandchildren.
• No two roots of trees have the same value.
• All the trees in the input are valid BSTs.
• 1 <= TreeNode.val <= 5 * 104.

Constructor Summary

Constructors

Constructor and Description
Solution()

Method Summary

Modifier and Type	Method and Description
TreeNode	canMerge(List<TreeNode> trees)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Solution

public Solution()

Method Detail

canMerge

public TreeNode canMerge(List<TreeNode> trees)