Overview

The root of a binary search tree is given. Two nodes of the binary search tree have been swapped. We need to fix the binary tree and recover the original structure

Program

Below is the program for the same

package main

import "fmt"

type TreeNode struct {
	Val   int
	Left  *TreeNode
	Right *TreeNode
}

func recoverTree(root *TreeNode) {
	var prev *TreeNode
	var first *TreeNode
	var mid *TreeNode
	var last *TreeNode

	recoverTreeUtil(root, &prev, &first, &mid, &last)

	if first != nil && last != nil {
		first.Val, last.Val = last.Val, first.Val
	} else if first != nil && mid != nil {
		first.Val, mid.Val = mid.Val, first.Val
	}
}

func recoverTreeUtil(root *TreeNode, prev, first, mid, last **TreeNode) {
	if root == nil {
		return
	}

	recoverTreeUtil(root.Left, prev, first, mid, last)

	if *prev == nil {
		*prev = root
	} else if *first == nil && (*prev).Val > root.Val {
		*first = *prev
		*mid = root
	} else if (*prev).Val > root.Val {
		*last = root
	}

	*prev = root

	recoverTreeUtil(root.Right, prev, first, mid, last)
}

func main() {
	root := TreeNode{Val: 2}
	root.Left = &TreeNode{Val: 3}
	root.Right = &TreeNode{Val: 1}

	recoverTree(&root)
	fmt.Println(root.Val)
	fmt.Println(root.Left.Val)
	fmt.Println(root.Right.Val)

}

Output

2
1
3

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