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en/codes/cpp/chapter_divide_and_conquer/build_tree.cpp
51 строка
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Yudong Jin
Translate all code to English (#1836)
31 дек 2025, 02:44
Не верифицирован
31 дек 2025, 02:44
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/** * File: build_tree.cpp * Created Time: 2023-07-17 * Author: krahets (krahets@163.com) */ #include "../utils/common.hpp" /* Build binary tree: divide and conquer */ TreeNode *dfs(vector<int> &preorder, unordered_map<int, int> &inorderMap, int i, int l, int r) { // Terminate when the subtree interval is empty if (r - l < 0) return NULL; // Initialize the root node TreeNode *root = new TreeNode(preorder[i]); // Query m to divide the left and right subtrees int m = inorderMap[preorder[i]]; // Subproblem: build the left subtree root->left = dfs(preorder, inorderMap, i + 1, l, m - 1); // Subproblem: build the right subtree root->right = dfs(preorder, inorderMap, i + 1 + m - l, m + 1, r); // Return the root node return root; } /* Build binary tree */ TreeNode *buildTree(vector<int> &preorder, vector<int> &inorder) { // Initialize hash map, storing the mapping from inorder elements to indices unordered_map<int, int> inorderMap; for (int i = 0; i < inorder.size(); i++) { inorderMap[inorder[i]] = i; } TreeNode *root = dfs(preorder, inorderMap, 0, 0, inorder.size() - 1); return root; } /* Driver Code */ int main() { vector<int> preorder = {3, 9, 2, 1, 7}; vector<int> inorder = {9, 3, 1, 2, 7}; cout << "Preorder traversal = "; printVector(preorder); cout << "Inorder traversal = "; printVector(inorder); TreeNode *root = buildTree(preorder, inorder); cout << "The constructed binary tree is:\n"; printTree(root); return 0; }