LEETCODE之Unique Binary Search Trees

Unique Binary Search Trees

https://leetcode.com/problems/unique-binary-search-trees/

动态规划，主要是迭代公式，代码如下

class Solution {public:    int numTrees(int n) {    int i, j, dp[n + 1];    if (n == 0) return 1;    dp[0] = dp[1] = 1;    for (i = 2; i <= n; i++) {        dp[i] = 0;        for (j = 0; j < i; j++) {            dp[i] += dp[j] * dp[i - j - 1];        }    }    return dp[n];}};

Unique Binary Search Trees II

https://leetcode.com/problems/unique-binary-search-trees-ii/

先记下，以后研究，代码如下

/*************************************************************************    > File Name: Solution.cpp    > Author: Duke-wei    > Mail: [e-mail]     > Created Time: Wed 28 Sep 2016 09:47:55 AM CST ************************************************************************/#include<iostream>using namespace std;//递归一波看看，给力//class Solution{public:<TreeNode*> generateTrees(int n2,int n1=1){<TreeNode*> TreeHeads;for(int i=n1;i<=n2;++i){auto LeftTrees = i==n1?<TreeNode*>(nullptr):generateTrees(i-1,n1);auto RightTrees = i==n2?<TreeNode*>(nullptr):generateTrees(n2,i+1);for(auto pleft:LeftTrees){for(auto pright:RightTrees){auto head = new TreeNode();head->left = pleft;head->right=pright;TreeHeads.push_back(head);}}}return TreeHeads;}};class Solution2{public:TreeNode* clone(TreeNode* root){if(root == nullptr)return nullptr;TreeNode* newroot = new TreeNode(root->val);newroot->left = clone(root->left);newroot->right = clone(root->right);return newroot;}vector<TreeNode *> generateTrees(int n) {vector<TreeNode *> res;if(n==0)return res;res.push_back(nullptr);for(int i = 1; i <= n; i++){vector<TreeNode *> tmp;for(int j = 0; j<res.size();j++){TreeNode* oldroot = res[j];TreeNode* root = new TreeNode(i);TreeNode* target = clone(oldroot);root->left = target;tmp.push_back(root);if(oldroot!=nullptr){TreeNode* tmpold = oldroot;while(tmpold->right!=nullptr){TreeNode* nonroot = new TreeNode(i);TreeNode *tright = tmpold->right;tmpold->right = nonroot;nonroot->left = tright;TreeNode *target = clone(oldroot);tmp.push_back(target);tmpold->right = tright;tmpold = tmpold->right;}tmpold->right = new TreeNode(i);TreeNode *target = clone(oldroot);tmp.push_back(target);tmpold->right = nullptr;}}res=tmp;}return res;}};