[leetcode]96. Unique Binary Search Trees
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题目:
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
分析:任意一个节点都可以作为根节点,比他小的构成左子树,比他大的构成右子树。此题用递推。
代码:
class Solution {public: int numTrees(int n) { vector<int> nums(n+1,0); nums[0]=1; nums[1]=1; for(int i=2;i<=n;i++){ for(int j=0;j<i;j++){ nums[i]+=nums[j]*nums[i-j-1]; } } return nums[n]; }};
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