[Swift]LeetCode965. 单值二叉树 | Univalued Binary Tree

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A binary tree is univalued if every node in the tree has the same value.

Return true if and only if the given tree is univalued. 

Example 1:

Input: [1,1,1,1,1,null,1]
Output: true

Example 2:

Input: [2,2,2,5,2]
Output: false

Note:

1. The number of nodes in the given tree will be in the range [1, 100].
2. Each node's value will be an integer in the range [0, 99].

---

如果二叉树每个节点都具有相同的值，那么该二叉树就是单值二叉树。

只有给定的树是单值二叉树时，才返回 true；否则返回 false。

示例 1：

输入：[1,1,1,1,1,null,1]
输出：true

示例 2：

输入：[2,2,2,5,2]
输出：false

提示：

1. 给定树的节点数范围是 [1, 100]。
2. 每个节点的值都是整数，范围为 [0, 99] 。

---

12 ms

/**
 * 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 {
    var s:Set<Int> = Set<Int>()
    func isUnivalTree(_ root: TreeNode?) -> Bool {
        s.insert(root!.val)
        if root?.left != nil
        {
             isUnivalTree(root!.left)
        }
        if root?.right != nil
        {
             isUnivalTree(root!.right)
        }
        return s.count == 1
    }
}

---

12ms

/**
 * 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 isUnivalTree(_ root: TreeNode?) -> Bool {
        guard let root = root else { return false }
        return univalTreeHelper(root, val: root.val)
    }
    
    func univalTreeHelper(_ root: TreeNode?, val: Int) -> Bool {
        guard let root = root else { return true }
        var matches = root.val == val ? true : false
        return matches && univalTreeHelper(root.left, val: val) && univalTreeHelper(root.right, val: val) 
    }
}

---

16ms

/**
 * 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 isUnivalTree(_ root: TreeNode?) -> Bool {
        if root == nil {
            return true
        }
        return isUnivalTree(root!, root!.val)
    }
    
    func isUnivalTree(_ root: TreeNode?, _ value: Int) -> Bool {
        if root == nil {
            return true
        }
        
        if (root?.val != value) {
            return false
        }
        
        return isUnivalTree(root?.left, value) && isUnivalTree(root?.right, value)
    }
}

---

16ms

/**
 * 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 isUnivalTree(_ root: TreeNode?) -> Bool {
        if root == nil {
            return true
        }
        
        if root?.left != nil && root?.val != root?.left?.val {
            return false
        }
        
        if root?.right != nil && root?.val != root?.right?.val {
            return false
        }
        
        return isUnivalTree(root?.left) && isUnivalTree(root?.right)
    }
}

---

20ms

/**
 * 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 isUnivalTree(_ root: TreeNode?) -> Bool {
        guard let root = root else { return false }
        return univalTreeHelper(root, val: root.val)
    }
    
    func univalTreeHelper(_ root: TreeNode?, val: Int) -> Bool {
        guard let root = root else { return true }
        var matches = root.val == val ? true : false
        return matches && univalTreeHelper(root.left, val: val) && univalTreeHelper(root.right, val: val) 
    }
}