use std::collections::HashMap;

impl Solution {
    pub fn subarray_sum(nums: Vec<i32>, k: i32) -> i32 {
        let (mut ans, mut sum) = (0, 0);
        let mut map = HashMap::new();
        map.insert(0, 1);
        for i in 0..nums.len() {
            sum += nums[i];
            map.entry(sum - k).or_insert(0);
            ans += map[&(sum - k)];
            map.entry(sum).or_insert(0);
            *map.get_mut(&sum).unwrap() += 1;
        }
        return ans;
    }
}

// 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;

use std::collections::VecDeque;

impl Solution {
    pub fn average_of_levels(root: Option<Rc<RefCell<TreeNode>>>) -> Vec<f64> {
        let mut ans = vec![];
        if root.is_none() {
            return ans;
        }

        let mut q = VecDeque::new();
        q.push_back(root.clone());
        while !q.is_empty() {
            let size = q.len();
            let mut sum : i64 = 0;
            let mut i = size;
            while i != 0 {
                if let Some(node) = q.pop_front() {
                    sum += node.clone().unwrap().borrow().val as i64;
                    let (left, right) = (
                        node.clone().unwrap().borrow().left.clone(),
                        node.clone().unwrap().borrow().right.clone()
                    );
                    if !left.is_none() {
                        q.push_back(left);
                    }
                    if !right.is_none() {
                        q.push_back(right);
                    }
                    i -= 1;
                }
            }
            ans.push(sum as f64 / size as f64);
        }
        return ans;
    }
}

// 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);
    }
}