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
翻译
给定n,存储值1 ... n的结构唯一BST(二进制搜索树)有多少?
例如,
给定n = 3,共有5个独特的BST。
分析
- 要求返回一个特定值,即通过观察这种特殊的BST结构,找出规律,找出对应的f[n]值。
- 以1为根的有两个,有2为根的有一个,以3为根的有两个。
- 其中以1为根的都只有一个子树有两个元素,
- 以2为根则是两个子树都有1个元素,
- 以3为根只有一个子树有两个元素。
f(0)=1;f(1)=1;
f(2)=f(0)*(1)+f(1)*f(0);
f(3)=f(0)*f(2)+f(1)*f(1)+f(2)*f(0)
百度一下
class Solution {public: int numTrees(int n) { vector<int> f(n+1,0); f[0] = 1; f[1] = 1; for(int i = 2;i <= n;i++){ for(int j = 1;j <= i;j++){ f[i] += f[j-1] * f[i-j]; }//for }//for return f[n]; }};
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- 96.Unique Binary Search Trees
- 96. Unique Binary Search Trees
- 96. Unique Binary Search Trees
- 96. Unique Binary Search Trees
- 96. Unique Binary Search Trees
- 96. Unique Binary Search Trees
- 96. Unique Binary Search Trees
- 96. Unique Binary Search Trees
- 96. Unique Binary Search Trees
- 96. Unique Binary Search Trees
- 96. Unique Binary Search Trees
- 96. Unique Binary Search Trees
- 96. Unique Binary Search Trees
- 96. Unique Binary Search Trees
- 96. Unique Binary Search Trees
- 96. Unique Binary Search Trees
- 96. Unique Binary Search Trees
- 96. Unique Binary Search Trees
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