binary search trees let binary search for fast lookup, addition and removal of data items, and can be used to implement dynamic sets and lookup tables. In computer science, a binary search tree (BST), also named an ordered or sorted binary tree, is a rooted binary tree whose internal nodes each shop a key greater than all the keys in the node's leave subtree and less than those in its right subtree.

COMING SOON!

```
class Solution {
public:
int numTrees(int n) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
vector<int> dp(n + 1, 0);
dp[0] = dp[1] = 1;
for (int i = 2; i <= n; i++) {
for (int j = 0; j < i; j++)
dp[i] += dp[j] * dp[i-j-1];
}
return dp[n];
}
};
```