889. Construct Binary Tree from Preorder and Postorder Traversal
Return any binary tree that matches the given preorder and postorder traversals.
Values in the traversals pre
and post
are distinct positive integers.
Example 1:
Input: pre = [1,2,4,5,3,6,7], post = [4,5,2,6,7,3,1] Output: [1,2,3,4,5,6,7]
Note:
1 <= pre.length == post.length <= 30
pre[]
andpost[]
are both permutations of1, 2, ..., pre.length
.- It is guaranteed an answer exists. If there exists multiple answers, you can return any of them.
Rust Solution
struct Solution;
use rustgym_util::*;
impl Solution {
fn construct_from_pre_post(pre: Vec<i32>, post: Vec<i32>) -> TreeLink {
Self::build(&mut 0, &mut 0, &pre, &post)
}
fn build(i: &mut usize, j: &mut usize, pre: &[i32], post: &[i32]) -> TreeLink {
let val = pre[*i];
*i += 1;
let mut left = None;
let mut right = None;
if val != post[*j] {
left = Self::build(i, j, pre, post);
}
if val != post[*j] {
right = Self::build(i, j, pre, post);
}
*j += 1;
tree!(val, left, right)
}
}
#[test]
fn test() {
let pre = vec![1, 2, 4, 5, 3, 6, 7];
let post = vec![4, 5, 2, 6, 7, 3, 1];
let res = tree!(
1,
tree!(2, tree!(4), tree!(5)),
tree!(3, tree!(6), tree!(7))
);
assert_eq!(Solution::construct_from_pre_post(pre, post), res);
}
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