LeetCode Entry

1022. Sum of Root To Leaf Binary Numbers

24.02.2026 easy 2026 kotlin rust

Sum of a binary numbers in a binary tree

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Problem TLDR

Sum of a binary numbers in a binary tree #easy

Intuition

The simplest way: helper method, global sum variable, track leafs.

Approach

• we can skip checking the leafs
• we can use tree itself as a storage

Complexity

• Time complexity: \(O(n)\)

• Space complexity: \(O(log(n))\)

Code

// 18ms
    fun sumRootToLeaf(r: TreeNode?): Int = r?.run {
        max(`val`, setOf(left,right).sumOf { it?.`val` += `val`*2; sumRootToLeaf(it) })
    } ?: 0

// 0ms
    pub fn sum_root_to_leaf(r: Option<Rc<RefCell<TreeNode>>>) -> i32 {
        r.map_or(0, |n| { let n = n.borrow_mut();
            [&n.left, &n.right].into_iter().flatten().map(|x| {
                x.borrow_mut().val += n.val * 2;
                Self::sum_root_to_leaf(Some(x.clone()))}).sum::<i32>().max(n.val)
        })
    }