Kth largest sum in a binary tree

Tree Breadth-First Search Sorting Binary Tree

59.0% acceptance

Feb 25, 2026

1072

You are given the root of a binary tree and a positive integer k. The level sum in the tree is the sum of the values of the nodes that are on the same level. Return the kth largest level sum in the tree (not necessarily distinct). If there are fewer than k levels in the tree, return -1. Note that two nodes are on the same level if they have the same distance from the root.

Solution

Rust

Time O(n²)

Space O(n)

LeetCode

solution.rs

use std::rc::Rc;
use std::cell::RefCell;
impl Solution {
  pub fn kth_largest_level_sum(root: Option<Rc<RefCell<TreeNode>>>, k: i32) -> i64 {
    use std::collections::VecDeque;
    let mut level_sums = Vec::new();
    let mut queue = VecDeque::new();
    if let Some(r) = root { queue.push_back(r); }
    while !queue.is_empty() {
      let level_size = queue.len();
      let mut sum = 0i64;
      for _ in 0..level_size {
        let node = queue.pop_front().unwrap();
        let n = node.borrow();
        sum += n.val as i64;
        if let Some(l) = n.left.clone() { queue.push_back(l); }
        if let Some(r) = n.right.clone() { queue.push_back(r); }
      }
      level_sums.push(sum);
    }
    let k = k as usize;
    if k > level_sums.len() { return -1; }
    level_sums.sort_unstable_by(|a, b| b.cmp(a));
    level_sums[k - 1]
  }
}