Package g1901_2000.s1932_merge_bsts_to_create_single_bst

Class 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 Detail

      • Solution

        public Solution()