Construct Binary Tree from Inorder and Postorder Traversal

题目介绍

LeetCode 106. Construct Binary Tree from Inorder and Postorder 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(_ inorder: [Int], _ postorder: [Int]) -> TreeNode? {
        guard !inorder.isEmpty else {
            return nil
        }
        let root = TreeNode(postorder.last!)
        let index = inorder.firstIndex(of: root.val)!
        root.left = buildTree(index.distance(to: 0) < 0 ? Array(inorder[0..<index]) : [], index.distance(to: 0) < 0 ? Array(postorder[0..<index]) : [])
        root.right = buildTree(index.distance(to: inorder.count-1) > 0 ? Array(inorder[index+1..<inorder.count]) : [], index.distance(to: 0) <= 0 ? Array(postorder[index..<postorder.count-1]) : [])
        return root
    }
}

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