Two nodes of a BST are swapped, correct the BST

Given a Binary Search Tree with two of the nodes of the Binary Search Tree (BST) swapped. The task is to fix (or correct) the BST.

Note: The BST will not have duplicates.

Examples:

Input Tree:
         10
        /  \
       5    8
      / \
     2   20

In the above tree, nodes 20 and 8 must be swapped to fix the tree.  
Following is the output tree
         10
        /  \
       5    20
      / \
     2   8

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach :

Traverse the BST in In-order fashion and store the nodes in a vector.
Then this vector is sorted after creating a copy of it.
Use Insertion sort as it works the best and fastest when the array is almost sorted. As in this problem, only two elements will be displaced so Insertion sort here will work in linear time.
After sorting, compare the sorted vector and the copy of the vector created earlier, by this, find out the error-some nodes and fix them by finding them in the tree and exchanging them.

Below is the implementation of above approach:

// C++ implementation of the above approach 
#include <bits/stdc++.h> 
using namespace std; 
   
// A binary tree node has data, pointer  
// to left child and a pointer to right child  
struct node { 
    int data; 
    struct node *left, *right; 
    node(int x) 
    { 
        data = x; 
        left = right = NULL; 
    } 
}; 
   
// Utility function for insertion sort 
void insertionSort(vector<int>& v, int n) 
{ 
    int i, key, j; 
    for (i = 1; i < n; i++) { 
        key = v[i]; 
        j = i - 1; 
        while (j >= 0 && v[j] > key) { 
            v[j + 1] = v[j]; 
            j = j - 1; 
        } 
        v[j + 1] = key; 
    } 
} 
   
// Utility function to create a vector  
// with inorder traversal of a binary tree 
void inorder(node* root, vector<int>& v) 
{ 
    // Base cases 
    if (!root) 
        return; 
   
    // Recurive call for left subtree 
    inorder(root->left, v); 
   
    // Insert node into vector 
    v.push_back(root->data); 
   
    // Recursive call for right subtree 
    inorder(root->right, v); 
} 
   
// Function to exchange data  
// for incorrect nodes 
void find(node* root, int res, int res2) 
{ 
    // Base cases 
    if (!root) { 
        return; 
    } 
   
    // Recurive call to find  
    // the node in left subtree 
    find(root->left, res, res2); 
   
    // Check if current node  
    // is incorrect and exchange 
    if (root->data == res) { 
        root->data = res2; 
    } 
    else if (root->data == res2) { 
        root->data = res; 
    } 
   
    // Recurive call to find  
    // the node in right subtree 
    find(root->right, res, res2); 
} 
   
// Primary function to fix the two nodes 
struct node* correctBST(struct node* root) 
{ 
    // Vector to store the  
    // inorder traversal of tree 
    vector<int> v; 
   
    // Function call to insert 
    // nodes into vector 
    inorder(root, v); 
   
    // create a copy of the vector 
    vector<int> v1 = v; 
   
    // Sort the original vector thereby  
    // making it a valid BST's inorder 
    insertionSort(v, v.size()); 
   
    // Traverse through both vectors and 
    // compare misplaced values in original BST 
    for (int i = 0; i < v.size(); i++) { 
  
        // Find the mismatched values 
        // and interchange them 
        if (v[i] != v1[i]) { 
  
            // Find and exchange the  
            // data of the two nodes 
            find(root, v1[i], v[i]); 
   
            // As it given only two values are  
            // wrong we don't need to check further 
            break; 
        } 
    } 
   
    // Return the root of corrected BST 
    return root; 
} 
  
// A utility function to 
// print Inoder traversal  
void printInorder(struct node* node) 
{ 
    if (node == NULL) 
        return; 
    printInorder(node->left); 
    printf("%d ", node->data); 
    printInorder(node->right); 
} 
   
int main() 
{  
    struct node* root = new node(6); 
    root->left = new node(10); 
    root->right = new node(2); 
    root->left->left = new node(1); 
    root->left->right = new node(3); 
    root->right->right = new node(12); 
    root->right->left = new node(7); 
   
    printf("Inorder Traversal of the 
                           original tree \n"); 
  
    printInorder(root); 
   
    correctBST(root); 
   
    printf("\nInorder Traversal of the  
                              fixed tree \n"); 
  
    printInorder(root); 
   
    return 0; 
} 

Time Complexity: O(N)
Auxiliary Space: O(N)
where N is the number of nodes in the Binary Tree.

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My Personal Notes

Two nodes of a BST are swapped, correct the BST | Set-2

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

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