[Swift]LeetCode700. 二叉搜索树中的搜索 | Search in a Binary Search Tree

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Given the root node of a binary search tree (BST) and a value. You need to find the node in the BST that the node's value equals the given value. Return the subtree rooted with that node. If such node doesn't exist, you should return NULL.

For example, 

Given the tree:
        4
       / 
      2   7
     / 
    1   3

And the value to search: 2

You should return this subtree:

      2     
     /    
    1   3

In the example above, if we want to search the value 5, since there is no node with value 5, we should return NULL.

Note that an empty tree is represented by NULL, therefore you would see the expected output (serialized tree format) as [], not null.

---

 给定二叉搜索树（BST）的根节点和一个值。 你需要在BST中找到节点值等于给定值的节点。 返回以该节点为根的子树。 如果节点不存在，则返回 NULL。

例如，

给定二叉搜索树:

        4
       / 
      2   7
     / 
    1   3

和值: 2

你应该返回如下子树:

      2     
     /    
    1   3

在上述示例中，如果要找的值是 5，但因为没有节点值为 5，我们应该返回 NULL。

---

Runtime: 168 ms

Memory Usage: 19.6 MB

/**
 * 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 searchBST(_ root: TreeNode?, _ val: Int) -> TreeNode? {
        var root = root
        while ((root != nil) && root!.val != val)
        {
            root = (root!.val > val) ? root?.left : root?.right
        }
        return root
    }
}

---

168ms

/**
 * 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 searchBST(_ root: TreeNode?, _ val: Int) -> TreeNode? {
        if nil == root {
            return nil
        } else{
            let value = (root?.val)!
            if value == val {
                return root
            } else if value < val {
                return searchBST(root?.right, val)
            } else {
                return searchBST(root?.left, val)
            }
        }
    }
}

---

188ms

/**
 * 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 searchBST(_ root: TreeNode?, _ val: Int) -> TreeNode? {
        guard root != nil else { return nil }
        var current = root
        while current != nil {
            if current!.val == nil { return nil }
            if current!.val == val { return current }
            if val > current!.val {
                current = current!.right
            } else {
                current = current!.left
            }
        }
        return nil
    }
}