Swift 将有序数组转换为二叉搜索树 - LeetCode

      0
     / \
   -3   9
   /   /
 -10  5

      0
    /   \
  -8      3
  / \    /  \
-10  5  1     9

/**
 * 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 sortedArrayToBST(_ nums: [Int]) -> TreeNode? {
        if nums.isEmpty { return nil }
        return getTree(nums, 0, nums.count - 1)
    }
    
    func getTree(_ nums: [Int], _ left: Int, _ right: Int) -> TreeNode? {
        guard left <= right else { return nil }
        let mid = (left + right) / 2
        let node = TreeNode(nums[mid])
        //对mid索引的处理不能忘记
        node.left = getTree(nums, left, mid - 1)
        node.right = getTree(nums, mid + 1, right)
        return node
    }
}