Print Binary Tree
按照要求输出二叉树在对应二维数组种的值

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public var val: Int
 *     public var left: TreeNode?
 *     public var right: TreeNode?
 *     public init(_ val: Int) {
 *         self.val = val
 *         self.left = nil
 *         self.right = nil
 *     }
 * }
 */
class Solution {
    func printTree(_ root: TreeNode?) -> [[String]] {
        let height = getHeight(root);
        let width = 1<<height - 1 
        var ans = Array(repeating: Array(repeating: "", count: width), count: height)
        fill(root, ans: &ans, h: 0, l: 0, r: width - 1)
        return ans
    }
  // 递归获取二叉树的高度  如果二叉树的右字数为空  则当前高度为 1 .. 反之.. 最后求得最大的左右字数的高度 + 1
    func getHeight(_ root: TreeNode?) -> Int {
        guard let r = root else { return 0 }
        return max(getHeight(r.left), getHeight(r.right)) + 1
    }
  // 递归填充结果数组
    func fill(_ root: TreeNode?, ans: inout [[String]],  h: Int, l: Int, r: Int) -> [[String]] { 
        guard let ro = root else { return ans }
        let mid = (l + r) / 2
        ans[h][mid] = "\(ro.val)"
        fill(ro.left, ans: &ans, h: h + 1, l: l, r: mid - 1)
        fill(ro.right, ans: &ans, h: h + 1, l: mid + 1, r: r)
        return ans
    }
}