1. Title
Given an integer n, generate all binary search trees consisting of 1… n nodes .
示例:
输入: 3
输出:
[
[1,null,3,2],
[3,2,null,1],
[3,1,null,null,2],
[2,1,3],
[1,null,2,null,3]
]
解释:
以上的输出对应以下 5 种不同结构的二叉搜索树:
1 3 3 2 1
\ / / / \ \
3 2 1 1 3 2
/ / \ \
2 1 2 3
Source: LeetCode
Link: https://leetcode-cn.com/problems/unique-binary-search-trees-ii The
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2. Problem solving
Similar questions:
Programmer Interview Gold Code-Interview Question 04.09. Binary search tree sequence (double-ended queue + backtracking) **
LeetCode 96. Different binary search tree (DP)
- Traverse each point of data [1, n], split into two halves, and generate recursively
class Solution {
public:
vector<TreeNode*> generateTrees(int n) {
if(n == 0)
return {};
return generateTrees(1,n);
}
vector<TreeNode*> generateTrees(int start, int end)
{
vector<TreeNode*> ans;
if(start > end)
{
ans.push_back(NULL);
return ans;
}
vector<TreeNode*> subLeft, subRight;
TreeNode *node;
for(int i = start; i <= end; i++)
{
subLeft = generateTrees(start,i-1);
subRight = generateTrees(i+1,end);
for(TreeNode* l : subLeft)
for(TreeNode* r : subRight)
{
node = new TreeNode(i);
node->left = l;
node->right = r;
ans.push_back(node);
}
}
return ans;
}
};
36 ms 17.7 MB