58 lines
1.7 KiB
Rust
58 lines
1.7 KiB
Rust
/*
|
|
* File: build_tree.rs
|
|
* Created Time: 2023-07-15
|
|
* Author: codingonion (coderonion@gmail.com)
|
|
*/
|
|
|
|
use std::collections::HashMap;
|
|
use std::{cell::RefCell, rc::Rc};
|
|
include!("../include/include.rs");
|
|
use tree_node::TreeNode;
|
|
|
|
/* Build binary tree: Divide and conquer */
|
|
fn dfs(
|
|
preorder: &[i32],
|
|
inorder_map: &HashMap<i32, i32>,
|
|
i: i32,
|
|
l: i32,
|
|
r: i32,
|
|
) -> Option<Rc<RefCell<TreeNode>>> {
|
|
// Terminate when subtree interval is empty
|
|
if r - l < 0 {
|
|
return None;
|
|
}
|
|
// Initialize root node
|
|
let root = TreeNode::new(preorder[i as usize]);
|
|
// Query m to divide left and right subtrees
|
|
let m = inorder_map.get(&preorder[i as usize]).unwrap();
|
|
// Subproblem: build left subtree
|
|
root.borrow_mut().left = dfs(preorder, inorder_map, i + 1, l, m - 1);
|
|
// Subproblem: build right subtree
|
|
root.borrow_mut().right = dfs(preorder, inorder_map, i + 1 + m - l, m + 1, r);
|
|
// Return root node
|
|
Some(root)
|
|
}
|
|
|
|
/* Build binary tree */
|
|
fn build_tree(preorder: &[i32], inorder: &[i32]) -> Option<Rc<RefCell<TreeNode>>> {
|
|
// Initialize hash table, storing in-order elements to indices mapping
|
|
let mut inorder_map: HashMap<i32, i32> = HashMap::new();
|
|
for i in 0..inorder.len() {
|
|
inorder_map.insert(inorder[i], i as i32);
|
|
}
|
|
let root = dfs(preorder, &inorder_map, 0, 0, inorder.len() as i32 - 1);
|
|
root
|
|
}
|
|
|
|
/* Driver Code */
|
|
fn main() {
|
|
let preorder = [3, 9, 2, 1, 7];
|
|
let inorder = [9, 3, 1, 2, 7];
|
|
println!("In-order traversal = {:?}", preorder);
|
|
println!("Pre-order traversal = {:?}", inorder);
|
|
|
|
let root = build_tree(&preorder, &inorder);
|
|
println!("The built binary tree is:");
|
|
print_util::print_tree(root.as_ref().unwrap());
|
|
}
|