Interactive Problems in Competitive Programming

Interactive Problems are those problems in which our solution or code interacts with the judge in real time. When we develop a solution for an Interactive Problem then the input data given to our solution may not be predetermined but is built for that problem specifically. The solution performs a series of exchange of data with the judge and at the end of the conversation the judge decides whether our solution was correct or not.

Guessing the Number (An Interactive Problem)

In this problem the user has to guess the number during a communication with the judge. The user is provided with the upper and lower bound and he/she can ask the judge whether a number is the number to be guessed. The judge replies with -1 if the number is smaller than the number to be guessed or 1 if number is greater than the number to be guessed or 0 if it is equal to the number to be guessed.

Approach 1 : Linear Guessing

The user can query the judge for all the numbers between lower limit and upper limit to find the solution.
Approach 1



filter_none

edit
close

play_arrow

link
brightness_4
code

import java.util.*;
class GFG {
    public static void main(String[] args)
    {
        Scanner sc1 = new Scanner(System.in);
        int lower_bound = 2;
        int upper_bound = 10;
  
        // Number to be guessed is 6
  
        // Iterating from lower_bound to upper_bound
        for (int i = lower_bound; i <= upper_bound; i++) {
            System.out.println(i);
  
            // Input the response from the judge
            int response = sc1.nextInt();
  
            if (response == 0) {
                System.out.println("Number guessed is :" + i);
                break;
            }
        }
    }
}

chevron_right






                        filter_none








Time Complexity: O(n)



Approach 2 : Applying Binary Search




We can also apply binary search interactively to find the solution. This solution is efficient as compared to the previous approach.













                                    filter_none




                                    edit

                                    close




                                    play_arrow




                                    link

                                    brightness_4

                                    code
                                




















import java.util.*; 


class GFG { 


    public static void main(String[] args) 


    { 


        Scanner sc1 = new Scanner(System.in); 


        int lower_bound = 2; 


        int upper_bound = 10; 


  


        // Number to be guessed is 9 


  


        // Applying Binary Search interactively 


        while (lower_bound <= upper_bound) { 


            int mid = (lower_bound + upper_bound) / 2; 


  


            // Print the guessed number 


            System.out.println(mid); 


  


            // Input the response from the judge 


            int response = sc1.nextInt(); 


  


            if (response == -1) { 


                lower_bound = mid + 1; 


            } 


            else if (response == 1) { 


                upper_bound = mid - 1; 


            } 


            else if (response == 0) { 


                System.out.println("Number guessed is :" + mid); 


                break; 


            } 


        } 


    } 


} 



















                        chevron_right







                        filter_none








Time Complexity: O(logn)

Algorithm Paradigm: Divide and Conquer



          
          
          

          

    

        My Personal Notes
        arrow_drop_up
    

    

        
        

            
            
        

    


Recommended Posts:
SauravPrateek
Check out this Author's contributed articles.
If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please Improve this article if you find anything incorrect by clicking on  the "Improve Article" button below.