55-I.二叉树的深度
一、 题目
输入一棵二叉树的根节点,求该树的深度。从根节点到叶节点依次经过的节点(含根、叶节点)形成树的一条路径,最长路径的长度为树的深度。
例如:
给定二叉树 [3,9,20,null,null,15,7],
3
/ \
9 20
/ \
15 7
返回它的最大深度 3 。
提示:
节点总数 <= 10000
来源:力扣(LeetCode)
链接:https://leetcode-cn.com/problems/er-cha-shu-de-shen-du-lcof
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二、 解法
2.1 递归
func maxDepth(_ root: TreeNode?) -> Int {
guard let tree = root else { return 0 }
if tree.left == nil, tree.right == nil { return 1 }
return max(maxDepth(tree.left), maxDepth(tree.right)) + 1
}
2.2 非递归
func maxDepth(_ root: TreeNode?) -> Int {
var deep = 0
guard let root = root else { return deep }
var queue: [TreeNode] = [root]
var currentLevelCount = 1
var nextLevelCount = 0
while queue.isEmpty == false {
let current = queue.removeFirst()
currentLevelCount -= 1
if let left = current.left {
queue.append(left)
nextLevelCount += 1
}
if let right = current.right {
queue.append(right)
nextLevelCount += 1
}
if currentLevelCount == 0 {
deep += 1
currentLevelCount = nextLevelCount
nextLevelCount = 0
}
}
return deep
}
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