1. Topic introduction
Traverse an array from left to right, and gradually generate a binary search tree by continuously inserting elements into the tree. Given a binary search tree composed of different nodes, output all possible arrays of this tree.
Example:
Given the following binary tree
2
/ \
1 3
return:
[
[2,1,3],
[2,3,1]
]
Source: LeetCode
Link: https://leetcode-cn.com/problems/bst-sequences-lcci
Copyright is owned by LeetCode . For commercial reprints, please contact the official authorization. For non-commercial reprints, please indicate the source.
Two, problem-solving ideas
This question is equivalent to investigating the full arrangement in disguise, and the method used is "backtracking + recursion + double-ended queue". This method has not been figured out by myself, and I can learn from others, and record it here.
Three, problem-solving code
class Solution {
public:
vector<vector<int>> BSTSequences(TreeNode* root) {
vector<vector<int>> res;
if(!root)
return {
{}};
vector<int> ans;
deque<TreeNode*> q;
q.push_back(root);
dfs(ans, res, q);
return res;
}
void dfs(vector<int>& ans, vector<vector<int>> &res, deque<TreeNode*>& q)
{
if(q.empty())
{
res.push_back(ans);
return;
}
for(int i = q.size(); i > 0; --i)
{
TreeNode* cur = q.front();
q.pop_front();
ans.push_back(cur->val);
int count = 0;
if(cur->left)
{
q.push_back(cur->left);
++count;
}
if(cur->right)
{
q.push_back(cur->right);
++count;
}
dfs(ans, res, q);
for(int j = 0; j < count; ++j)
q.pop_back();
ans.pop_back();
q.push_back(cur);
}
}
};Four, problem-solving results
