Unique Binary Search Trees I
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
Solution: dp.
http://fisherlei.blogspot.com/2013/03/leetcode-unique-binary-search-trees.html
1 class Solution { 2 public: 3 int numTrees(int n) { 4 vector<int> dp(n+1, 0); 5 dp[0] = 1; 6 dp[1] = 1; 7 for(int i = 2; i <= n; i++) { 8 for(int j = 0; j < i; j++) { 9 dp[i] += dp[j] * dp[i-j-1]; 10 } 11 } 12 return dp[n]; 13 } 14 };