Unique
Binary Search Trees:
Given n, how many structurally unique BST's (binary
search trees) that store values 1...n?
For example,
Given n = 3, there are a total of 5 unique BST's.
1 3 3 2 1 \ / / / \ \ 3 2 1 1 3 2 / / \ \ 2 1 2 3
其实就是计算卡特兰数。
class Solution { public: int numTrees(int n) { // Start typing your C/C++ solution below // DO NOT write int main() function if ( n<=0 ) return 0; vector<int> dp(n+1,0); dp[0]=1; for(int i=1;i<=n;i++) { for(int left=0;left<i;left++) { dp[i]+=dp[left]*dp[i-left-1]; } } return dp[n]; } };