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文章目录
  1. 题目介绍
  2. 复杂度
  3. 解题思路

Construct Binary Tree from Inorder and Postorder Traversal

题目介绍

LeetCode 105. Construct Binary Tree from Preorder and Inorder Traversal

复杂度

时间复杂度: O(n), 空间复杂度: O(n)

解题思路

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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 buildTree(_ preorder: [Int], _ inorder: [Int]) -> TreeNode? {
guard !preorder.isEmpty else {
return nil
}
let root = TreeNode(preorder.first!)
let index = inorder.firstIndex(of: root.val)!
root.left = buildTree(index.distance(to: 0) < 0 ? Array(preorder[1...index]) : [], index.distance(to: 0) < 0 ? Array(inorder[0..<index]) : [])
root.right = buildTree(index.distance(to: preorder.count) > 0 ? Array(preorder[index+1..<preorder.count]) : [], index.distance(to: inorder.count) > 0 ? Array(inorder[index+1..<inorder.count]) : [])
return root
}
}
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