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99 Recover Binary Search Tree.swift
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99 Recover Binary Search Tree.swift
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//
// 99 Recover Binary Search Tree.swift
// LeetCode-Solutions
//
// Created by Aleksandar Dinic on 31/10/2020.
// Copyright © 2020 Aleksandar Dinic. All rights reserved.
//
import Foundation
/// Source: https://leetcode.com/problems/recover-binary-search-tree/
class Solution {
private var first: TreeNode?
private var second: TreeNode?
private var prev = TreeNode(Int.min)
/// Recovers the tree without changing its structure where exactly two nodes of
/// the tree were swapped by mistake.
///
/// - Parameter root: Binary tree root.
///
/// - Complexity:
/// - time: O(n), where n is the number of nodes in the binary tree.
/// - space: O(h), where h is the height of the binary tree.
func recoverTree(_ root: TreeNode?) {
traverse(root)
guard let first = first, let second = second else { return }
let tmp = first.val
first.val = second.val
second.val = tmp
}
private func traverse(_ root: TreeNode?) {
guard let root = root else { return }
traverse(root.left)
if first == nil, prev.val >= root.val {
first = prev
}
if first != nil, prev.val >= root.val {
second = root
}
prev = root
traverse(root.right)
}
}
/// Provided code
public class TreeNode {
public var val: Int
public var left: TreeNode?
public var right: TreeNode?
public init() {
self.val = 0
self.left = nil
self.right = nil
}
public init(_ val: Int) {
self.val = val
self.left = nil
self.right = nil
}
public init(_ val: Int, _ left: TreeNode?, _ right: TreeNode?) {
self.val = val
self.left = left
self.right = right
}
}