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

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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