getKthCharacter that takes a RopeTreeNode and an integer k as arguments.null, return a placeholder character (e.g., \0).node.len == 0), return the character at index k-1 of node.val if k is within bounds.k with the len of the left child.k is less than or equal to the left child's len, recurse into the left child with k.k is greater than the left child's len, recurse into the right child with k adjusted by subtracting the left child's len.