96. Unique Binary Search Trees
Medium
Given an integer n
, return the number of structurally unique BST's (binary search trees) which has exactly n
nodes of unique values from 1
to n
.
Example 1:
Example 2:
Constraints:
1 <= n <= 19
解題
以不同的點當作中點,以 5 為例,左右子樹可能有以下情況:
合計 42 種可能
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