[LeetCode]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
思考:子问题分解,累加左孩子数*右孩子数。
class Solution { public: int numTrees(int n) { vector<int> dp(n+1,0); //vector<int> dp(n,0);初始化出错 dp[0]=1; dp[1]=1; for(int i=2;i<=n;i++) { for(int j=0;j<i;j++) dp[i]+=dp[j]*dp[i-1-j]; } return dp[n]; } };