LeetCode刷题（C++）——Construct Binary Tree from Preorder and Inorder Traversal（Normal）

题目描述

Given preorder and inorder traversal of a tree, construct the binary tree.

Note:

You may assume that duplicates do not exist in the tree.

/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
TreeNode* buildTree(vector<int>& preorder, vector<int>& inorder) {
if (preorder.size() == 0 || inorder.size() == 0 || preorder.size() != inorder.size())
return NULL;
return dfs(preorder, 0, preorder.size() - 1, inorder, 0, inorder.size() - 1);
}

TreeNode* dfs(vector<int>& preorder, int l1, int r1, vector<int>& inorder, int l2, int r2)
{
if (l1 > r1)
return NULL;
if (l1 == r1)
return new TreeNode(preorder[l1]);
TreeNode* root = new TreeNode(preorder[l1]);
for (int i = 0; i < inorder.size();i++)
{
if (inorder[i] == preorder[l1])
{
root->left = dfs(preorder, l1 + 1, l1 + i - l2, inorder, l2, i - 1);
root->right = dfs(preorder, l1 + i - l2 + 1, r1, inorder, i + 1, r2);
return root;
}
}
return NULL;
}
};