leetcode:构建二叉树

最新推荐文章于 2025-05-25 21:03:50 发布

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#leetcode #二叉树

本文详细介绍了如何使用中序和后序遍历序列构建二叉树，包括递归方法和核心逻辑解析。

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Construct Binary Tree from Inorder and Postorder Traversal

class Solution {

public:
TreeNode *buildTree(vector<int> &inorder, vector<int> &postorder) {
int len = postorder.size();
TreeNode *node = buildTree(inorder.begin(),inorder.end(),postorder.begin(),postorder.end());
return node;
}
private:
TreeNode *buildTree(vector<int>::iterator in_first,vector<int>::iterator in_last,vector<int>::iterator post_first,vector<int>::iterator post_last)
{
if(in_first == in_last)
return NULL;
if(post_first == post_last)
return NULL;

TreeNode *node = new TreeNode(*(post_last-1));
vector<int>::iterator it = find(in_first,in_last,*(post_last-1));
int leftSize = it - in_first;

node->left = buildTree(in_first,it,post_first,post_first+leftSize);
node->right = buildTree(it+1,in_last,post_first+leftSize,post_last-1);

return node;
}

};

Construct Binary Tree from Preorder and Inorder Traversal

class Solution {
public:
TreeNode *buildTree(vector<int> &preorder, vector<int> &inorder) {
TreeNode* node = buildTree(preorder.begin(),preorder.end(),inorder.begin(),inorder.end());
return node;
}
// template<typename InputIterator>
TreeNode* buildTree(vector<int>::iterator pre_first, vector<int>::iterator pre_last,vector<int>::iterator in_first, vector<int>::iterator in_last)
{
if(pre_first == pre_last)
return NULL;
if(in_first == in_last)
return NULL;

TreeNode* node = new TreeNode(*pre_first);
vector<int>::iterator root = find(in_first,in_last,*pre_first);
int leftSize = root - in_first;//distance(in_first,root);

node->left = buildTree(pre_first+1,pre_first+leftSize+1,in_first,root);
node->right = buildTree(pre_first+leftSize+1,pre_last,root+1,in_last);

return node;
}
};