Given the root
of a binary tree, the level of its root is 1
, the level of its children is 2
, and so on.
Return the smallest level x
such that the sum of all the values of nodes at level x
is maximal.
Example 1:
Input: root = [1,7,0,7,-8,null,null] Output: 2 Explanation: Level 1 sum = 1. Level 2 sum = 7 + 0 = 7. Level 3 sum = 7 + -8 = -1. So we return the level with the maximum sum which is level 2.
Example 2:
Input: root = [989,null,10250,98693,-89388,null,null,null,-32127] Output: 2
Constraints:
[1, 104]
.-105 <= Node.val <= 105
struct Solution;
use rustgym_util::*;
use std::collections::HashMap;
trait Preorder {
fn preorder(&self, level: usize, sum: &mut HashMap<usize, i32>);
}
impl Preorder for TreeLink {
fn preorder(&self, level: usize, sum: &mut HashMap<usize, i32>) {
if let Some(node) = self {
let val = node.borrow().val;
*sum.entry(level).or_default() += val;
let left = &node.borrow().left;
let right = &node.borrow().right;
left.preorder(level + 1, sum);
right.preorder(level + 1, sum);
}
}
}
impl Solution {
fn max_level_sum(root: TreeLink) -> i32 {
let mut sum = HashMap::new();
root.preorder(1, &mut sum);
*sum.iter().max_by_key(|(_, &v)| v).unwrap().0 as i32
}
}
#[test]
fn test() {
let root = tree!(1, tree!(7, tree!(7), tree!(-8)), tree!(0));
let res = 2;
assert_eq!(Solution::max_level_sum(root), res);
}