LeetCode 654. Maximum Binary Tree

Problem Statement

// Definition for a binary tree node.
// #[derive(Debug, PartialEq, Eq)]
// pub struct TreeNode {
//   pub val: i32,
//   pub left: Option<Rc<RefCell<TreeNode>>>,
//   pub right: Option<Rc<RefCell<TreeNode>>>,
// }
// 
// impl TreeNode {
//   #[inline]
//   pub fn new(val: i32) -> Self {
//     TreeNode {
//       val,
//       left: None,
//       right: None
//     }
//   }
// }
use std::rc::Rc;
use std::cell::RefCell;

impl Solution {
    fn dfs(nums: &Vec<i32>, start: usize, end: usize) -> Option<Rc<RefCell<TreeNode>>> {
        if start > end {
            return None;
        }
        let (mut val, mut index) = (std::i32::MAX, 0);
        for i in start..end + 1 {
            if nums[i] > val {
                val = nums[i];
                index = i;
            }
        }

        let mut node = TreeNode::new(val);
        node.left = Self::dfs(nums, start, index - 1);
        node.right = Self::dfs(nums, index + 1, end);
        return Some(Rc::new(RefCell::new(node)));
    }

    pub fn construct_maximum_binary_tree(nums: Vec<i32>) -> Option<Rc<RefCell<TreeNode>>> {
        return Self::dfs(&nums, 0, nums.len() - 1);
    }
}