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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