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【leetcode】Unique Binary Search Trees II
Unique Binary Search Trees II
Given n, generate all structurally unique BST‘s (binary search trees) that store values 1...n.
For example,
Given n = 3, your program should return all 5 unique BST‘s shown below.
1 3 3 2 1 \ / / / \ 3 2 1 1 3 2 / / \ 2 1 2 3
从1-n中选取一个元素i，i左边的元素都在左子树上，i右边的元素都在右子树上
1 /** 2 * Definition for binary tree 3 * struct TreeNode { 4 * int val; 5 * TreeNode *left; 6 * TreeNode *right; 7 * TreeNode(int x) : val(x), left(NULL), right(NULL) {} 8 * }; 9 */10 class Solution {11 public:12 vector<TreeNode *> generateTrees(int n) {13 14 vector<TreeNode *>result=build(1,n);15 return result;16 }17 18 vector<TreeNode *> build(int l,int r)19 {20 21 if(l>r)22 {23 vector<TreeNode *> root(1);24 root[0]=NULL;25 return root;26 }27 28 vector<TreeNode *> result;29 30 for(int i=l;i<=r;i++)31 {32 vector<TreeNode *> left=build(l,i-1);33 vector<TreeNode *> right=build(i+1,r);34 for(int j=0;j<left.size();j++)35 {36 for(int k=0;k<right.size();k++)37 {38 TreeNode *root=new TreeNode(i);39 root->left=left[j];40 root->right=right[k];41 result.push_back(root);42 43 }44 }45 }46 47 return result;48 }49 };
【leetcode】Unique Binary Search Trees II
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