LeetCode Entry

2265. Count Nodes Equal to Average of Subtree

10.09.2026 medium 2026 kotlin rust

Values equal subtree average

2265. Count Nodes Equal to Average of Subtree medium substack youtube

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Problem TLDR

Values equal subtree average

Intuition

Solve for subtree: count, sum, result

Approach

• pack two values into a single 32-bit int
• reuse the function by storing data in the tree itself

Complexity

• Time complexity: \(O(n)\)

• Space complexity: \(O(n)\)

Code

    fun averageOfSubtree(r: TreeNode?): Int = r?.run {
        val v = `val`
        val res = averageOfSubtree(left) + averageOfSubtree(right)
        `val` = (left?.`val` ?: 0) + (right?.`val` ?: 0) + 1 + v * 1024
        res + if (v == `val` / 1024 / (`val` % 1024)) 1 else 0
    } ?: 0

    pub fn average_of_subtree(r: Option<Rc<RefCell<TreeNode>>>) -> i32 {
        let Some(n) = r else {return 0}; let mut b = n.borrow_mut(); let v = b.val;
        let [l, r] = [&b.left, &b.right].map(|c|
            (Self::average_of_subtree(c.clone()), c.as_ref().map_or(0, |x| x.borrow().val)));
        let (c, s) = (l.1 % 1024 + r.1 % 1024 + 1, l.1 / 1024 + r.1 / 1024 + v);
        b.val = s * 1024 + c; l.0 + r.0 + (v == s / c) as i32
    }