Решение

class Solution {
    fun findTilt(root: TreeNode?): Int {
        var ans = 0
        fun dfs(node: TreeNode?): Int {
            if (node == null) return 0
            val l = dfs(node.left)
            val r = dfs(node.right)
            val d = l - r
            ans += if (d >= 0) d else -d
            return l + r + node.`val`
        }
        dfs(root)
        return ans
    }
}