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57 lines
1.6 KiB
57 lines
1.6 KiB
/*
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* File: build_tree.rs
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* Created Time: 2023-07-15
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* Author: codingonion (coderonion@gmail.com)
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*/
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use hello_algo_rust::include::{print_util, TreeNode};
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use std::collections::HashMap;
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use std::{cell::RefCell, rc::Rc};
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/* 构建二叉树：分治 */
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fn dfs(
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preorder: &[i32],
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inorder_map: &HashMap<i32, i32>,
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i: i32,
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l: i32,
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r: i32,
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) -> Option<Rc<RefCell<TreeNode>>> {
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// 子树区间为空时终止
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if r - l < 0 {
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return None;
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}
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// 初始化根节点
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let root = TreeNode::new(preorder[i as usize]);
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// 查询 m ，从而划分左右子树
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let m = inorder_map.get(&preorder[i as usize]).unwrap();
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// 子问题：构建左子树
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root.borrow_mut().left = dfs(preorder, inorder_map, i + 1, l, m - 1);
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// 子问题：构建右子树
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root.borrow_mut().right = dfs(preorder, inorder_map, i + 1 + m - l, m + 1, r);
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// 返回根节点
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Some(root)
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}
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/* 构建二叉树 */
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fn build_tree(preorder: &[i32], inorder: &[i32]) -> Option<Rc<RefCell<TreeNode>>> {
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// 初始化哈希表，存储 inorder 元素到索引的映射
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let mut inorder_map: HashMap<i32, i32> = HashMap::new();
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for i in 0..inorder.len() {
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inorder_map.insert(inorder[i], i as i32);
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}
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let root = dfs(preorder, &inorder_map, 0, 0, inorder.len() as i32 - 1);
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root
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}
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/* Driver Code */
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fn main() {
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let preorder = [3, 9, 2, 1, 7];
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let inorder = [9, 3, 1, 2, 7];
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println!("中序遍历 = {:?}", preorder);
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println!("前序遍历 = {:?}", inorder);
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let root = build_tree(&preorder, &inorder);
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println!("构建的二叉树为：");
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print_util::print_tree(root.as_ref().unwrap());
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}
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