Given a complete binary tree, count the number of nodes.
Note:
Definition of a complete binary tree from Wikipedia:
In a complete binary tree every level, except possibly the last, is completely filled, and all nodes in the last level are as far left as possible. It can have between 1 and 2h nodes inclusive at the last level h.
Example:
Input:
1
/ \
2 3
/ \ /
4 5 6
Output: 6给出一个完全二叉树，求出该树的节点个数。
说明：
完全二叉树的定义如下：在完全二叉树中，除了最底层节点可能没填满外，其余每层节点数都达到最大值，并且最下面一层的节点都集中在该层最左边的若干位置。若最底层为第 h 层，则该层包含 1~ 2h 个节点。
示例:
输入:
1
/ \
2 3
/ \ /
4 5 6
输出: 696ms
1 /** 2 * Definition for a binary tree node. 3 * public class TreeNode { 4 * public var val: Int 5 * public var left: TreeNode? 6 * public var right: TreeNode? 7 * public init(_ val: Int) { 8 * self.val = val 9 * self.left = nil 10 * self.right = nil 11 * } 12 * } 13 */ 14 class Solution { 15 func countNodes(_ root: TreeNode?) -> Int { 16 guard root != nil else{ 17 return 0 18 } 19 20 var leftCount = 0 21 var rightCount = 0 22 23 var leftNode = root 24 var rightNode = root 25 while leftNode != nil{ 26 leftCount += 1 27 leftNode = leftNode?.left 28 } 29 30 while rightNode != nil{ 31 rightCount += 1 32 rightNode = rightNode?.right 33 } 34 if leftCount == rightCount{ 35 return Int( pow(Double(2), Double(leftCount)) - 1.0) 36 } 37 38 return countNodes(root?.left) + countNodes(root?.right) + 1 39 40 } 41 }
100ms
1 /** 2 * Definition for a binary tree node. 3 * public class TreeNode { 4 * public var val: Int 5 * public var left: TreeNode? 6 * public var right: TreeNode? 7 * public init(_ val: Int) { 8 * self.val = val 9 * self.left = nil 10 * self.right = nil 11 * } 12 * } 13 */ 14 class Solution { 15 func countNodes(_ root: TreeNode?) -> Int { 16 guard let root = root else { return 0 } 17 18 return 1 + countNodes(root.left) + countNodes(root.right) 19 } 20 }
104ms
1 /** 2 * Definition for a binary tree node. 3 * public class TreeNode { 4 * public var val: Int 5 * public var left: TreeNode? 6 * public var right: TreeNode? 7 * public init(_ val: Int) { 8 * self.val = val 9 * self.left = nil 10 * self.right = nil 11 * } 12 * } 13 */ 14 class Solution { 15 var nodes = 0 16 17 func countNodes(_ root: TreeNode?) -> Int { 18 guard let root = root else { return 0 } 19 nodes += 1 20 if let left = root.left { 21 countNodes(left) 22 } 23 if let right = root.right { 24 countNodes(right) 25 } 26 return nodes 27 } 28 }
112ms
1 /** 2 * Definition for a binary tree node. 3 * public class TreeNode { 4 * public var val: Int 5 * public var left: TreeNode? 6 * public var right: TreeNode? 7 * public init(_ val: Int) { 8 * self.val = val 9 * self.left = nil 10 * self.right = nil 11 * } 12 * } 13 */ 14 class Solution { 15 func countNodes(_ root: TreeNode?) -> Int { 16 if root == nil { 17 return 0 18 } 19 var count = 0 20 var stack = [TreeNode?]() 21 stack.append(root) 22 while !stack.isEmpty { 23 guard let node = stack.removeLast() else { 24 return count 25 } 26 count += 1 27 if let lNode = node.left { 28 stack.append(lNode) 29 } 30 if let rNode = node.right { 31 stack.append(rNode) 32 } 33 } 34 return count 35 } 36 }
120ms
1 /** 2 * Definition for a binary tree node. 3 * public class TreeNode { 4 * public var val: Int 5 * public var left: TreeNode? 6 * public var right: TreeNode? 7 * public init(_ val: Int) { 8 * self.val = val 9 * self.left = nil 10 * self.right = nil 11 * } 12 * } 13 */ 14 class Solution { 15 func countNodes(_ root: TreeNode?) -> Int { 16 guard let root = root else { 17 return 0 18 } 19 20 let left = countLeftNodes(root) 21 let right = countRightNodes(root) 22 23 if left == right { 24 return NSDecimalNumber(decimal: Decimal(pow(2.0, Double(left)) - 1.0)).intValue 25 } 26 27 return countNodes(root.left) + countNodes(root.right) + 1 28 } 29 30 private func countLeftNodes(_ node: TreeNode?) -> Int { 31 var height = 0, node = node 32 33 while node != nil { 34 node = node?.left 35 height += 1 36 } 37 38 return height 39 } 40 41 private func countRightNodes(_ node: TreeNode?) -> Int { 42 var height = 0, node = node 43 while node != nil { 44 node = node?.right 45 height += 1 46 } 47 48 return height 49 } 50 }
176ms
1 /** 2 * Definition for a binary tree node. 3 * public class TreeNode { 4 * public var val: Int 5 * public var left: TreeNode? 6 * public var right: TreeNode? 7 * public init(_ val: Int) { 8 * self.val = val 9 * self.left = nil 10 * self.right = nil 11 * } 12 * } 13 */ 14 class Solution { 15 func countNodes(_ root: TreeNode?) -> Int { 16 var hLeft:Int = leftHeight(root) 17 var hRight:Int = rightHeight(root) 18 if hLeft == hRight 19 { 20 return Int(pow(Double(2), Double(hLeft)) - 1) 21 } 22 return countNodes(root!.left) + countNodes(root!.right) + 1 23 } 24 25 func leftHeight(_ root: TreeNode?) -> Int 26 { 27 if root == nil {return 0} 28 return 1 + leftHeight(root!.left) 29 } 30 31 func rightHeight(_ root: TreeNode?) -> Int 32 { 33 if root == nil {return 0} 34 return 1 + rightHeight(root!.right) 35 } 36 }
