96. Unique Binary Search Trees
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:
Input: n = 3
Output: 5
Example 2:
Input: n = 1
Output: 1
Constraints:
- 1 <= n <= 19
class Solution {
public int numTrees(int n) {
if(n==0||n==1){
return 1;
}
int[] res = new int[n+1];
res[0] = 1;
for(int i=1;i<=n;i++){
for(int j=0;j<i;j++){
res[i]+=res[j]*res[i-j-1];
}
}
return res[n];
}
}