Recover BST

Author: akashmodak97

Hacker Blocks/Recover BST.cpp

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+/* Hacker Blocks */
+/* Title -  Recover BST */
+/* Created By - Akash Modak */
+/* Date - 26/10/2020 */
+
+
+// Two elements of a binary search tree (BST) are swapped by mistake. Tell us the 2 values swapping which the tree will be restored.
+
+// Input Format
+// First line contains n denoting the input size.
+// Next line contains n space separated integers denoting the preorder input of the tree.
+
+// NOTE : -1 indicates that the node does not exist.
+
+// Constraints
+// 1 <= n <= 10^5
+// Your recovery algorithm should work in O(n) time.
+
+// Output Format
+// Print the two integers in space separated manner. The output should be sorted.
+
+// Sample Input
+// 3 2 1 -1 -1 -1 5 6 4 -1 -1 -1 -1 
+// Sample Output
+// 5 6
+// Explanation
+// The tree looks like
+
+//              3
+//           /      \
+//        2           5
+//     /            /    
+//    1           6      
+//              /
+//            4  
+// Swapping 5 and 6 makes the tree a BST.
+
+#include <bits/stdc++.h>
+using namespace std;
+vector<int> v;
+class node{
+    public:
+    int data;
+    node* left,*right;
+    node(int d){
+        data = d;
+        left=right=NULL;
+    }
+};
+node* build(){
+    int d;
+    cin>>d;
+    
+    if(d==-1){
+        return NULL;
+    }
+    node* root = new node(d);
+    root->left = build();
+    root->right = build();
+    return root;
+}
+void inorder(node* root){
+    if(root==NULL)
+    return;
+
+    inorder(root->left);
+    v.push_back(root->data);
+    inorder(root->right);
+}
+pair<int,int> checkSwap(){
+    int x=-1,y=-1,i;
+    for(i=0;i<v.size()-1;i++){
+        if(v[i+1]<v[i]){
+            y=v[i+1];
+            if(x==-1)
+            x=v[i];
+        }
+    }
+    return {x,y};
+}
+int main() {
+    /* code here */
+    node* root = build();
+    inorder(root);
+    pair<int,int> p = checkSwap();
+    cout<<min(p.first,p.second)<<" "<<max(p.first,p.second)<<endl;
+    return 0;
+}