I've just brute-forced answers for N = 2...500 and found the trick.
But how to prove it is always correct or, at least, for the given binary sequences?

What is test 8?
I tested my program for 9<=n<=200 brute force and my answers is right.
For 1<=n<=8 output is:
i : NO when i<=n-1
n: aaaaaaaa (n times)

The test is "abcdeedcbaabcdeedcba"(without quotes).
The answer should be ""(empty string).

hey if one else to know print the anser plese say me..in the test #4 i have a empty string, but the judge say me "wa" in test #4.... why??? help me please.

#include <bits/stdc++.h>
using namespace std;

int main(){
    string cad,res;
             cin>>cad;
             res = "";
    int tam = cad.length();
    int i,j;
        i=0; j=1;

    int boolean[tam]={0};

    while(j<tam){
        if(cad[i]==cad[j]){
            boolean[i] = 1;
            boolean[j] = 1;

            if(i-1>=0){
                i-=1;
                j+=1;
            }else{
                i=j+1;
                j+=2;
            }
        }else{
            i=j;
            j+=1;
        }
    }

    for(int i=0;i<tam;i++){
         if(boolean[i]==0)
             res+=cad[i];
     }
     cout<<res;
    return 0;
}

My algo generate array like [1, -1, 2, -2, 3, -3 ...,0], but i got WA27
Any suggetion's?
(Bad english)

Edited by author 25.08.2016 23:47

1. Answer always exists.
2. Use DFS for all unmarked vertices and mark them: if current vertex is marked as x, all next must be marked as (x + 1) % 2. (0->1, 1->0)
3. Then just print all vertices marked by 0 (or 1).

Don't use std::unordered_set as a hash table in C++. There is a test against it, so you'd better use your own hash table or use std::bitset.

Edited by author 27.08.2016 13:09

Edited by author 27.08.2016 13:09

недавно столкнулся с проблемой того что необходимо сохранять некоторыерешения на компьютер если для этого какие нибуть програмки?

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.Serialization;
using System.Runtime.Serialization.Formatters.Soap;
using System.IO;

namespace _2033
{
    class Device
    {
        public string Friend { get; set; }
        public string Name { get; set; }
        public int Cost { get; set; }
    }

    class Program
    {
        static void Main()
        {

            List<Device> objList = new List<Device>();
            for (int i = 0; i < 6; i++)
                objList.Add(new Device { Friend = Console.ReadLine(), Name = Console.ReadLine(),
                    Cost = int.Parse(Console.ReadLine()) });

            // 1. Находим девайс, который находится у большинства парней
            var query = from list in objList
                        group list by list.Name into grouping
                        orderby grouping.Count () descending
                        where
                        grouping.Count()>=2
                        select new {grouping.Key,PRCNT= grouping.Count ()} ;

            string Device = "";

            int prev_cnt = 0;
            bool isFind = true;
            foreach (var item in query)
            {
                if (prev_cnt != 0 && item.PRCNT == prev_cnt)
                {
                    isFind = false;
                    break;
                }
                else if (prev_cnt >= 2 && item.PRCNT<prev_cnt)
                    break;

                Device = item.Key;
                prev_cnt = item.PRCNT;
            }

            if (Device != "" && isFind)
            {
                Console.WriteLine(Device);
                return;
            }

            //Если таких устройств несколько , то находим самое дешевое из них

            var query2 = objList.OrderBy(dev => dev.Cost);
            foreach (var item in query2)
            {
                Console.WriteLine(item.Name);
                return;
            }
        }
    }
}

Samples:

1
201 405
Should be 99(2) + (3)

1
301 907
Should be 99(3) + (4)

1
448 2824
Should output something large, but the solution definitely exists :)

Edited by author 26.08.2016 07:23

Sample numbers have different value of math.sqrt() in last digit. Why? This task is not so big level for hidden problem.

 sample result:
2297.0716
936297014.1164
0.0000
37.7757

my result:
2297.0715
936297024.0000
0.0000
37.7757

import java.io.PrintWriter;
import java.util.Scanner;
import java.util.*;

public class AlgorithmTAsk {

    public static void main(String[] arg){

        Scanner in = new Scanner(System.in);
        PrintWriter out = new PrintWriter(System.out);
        ArrayList<Float> f = new ArrayList<Float>();

        while (in.hasNextLong()) {
            f.add((float) Math.sqrt(in.nextLong()));
        }

        for(int i = f.size()-1;i>=0;i--){
            out.printf("%8.6f\n",f.get(i));

        }

        out.flush();
    }
}

Edited by author 19.04.2016 19:45

in prims algo implementation using priority queue, how can i decrease a key in priority queue ?

I got AC on VB .NET 2010 !!!
Write me on mail saucy_smile@mail.ru and I'll send you the source code :-)

Edited by author 24.08.2016 08:07

Edited by author 24.08.2016 08:08

Please check the 12-th test. I and others thinks that our solutions are correct, but they are WA on 12...

Maybe anyone can give a little hint?

Edited by author 03.08.2006 16:49

I got AC when add:

if (Regex.Match(val, "[\\+\\-]?([0-9]*\\.)?[0-9]+([eE]?[\\+\\-]?[0-9]+)?", RegexOptions.Singleline).Value != val)
{
Console.WriteLine("Not a floating point number");
}

Hello! If you have WA 5, pay attention to the fact, that some programmer could take part in contests in more than 3 comands, even in all.

Got AC

if you WA #9
try this

0.00000000000e10
5
0.00000000001e10
5

Hello everybody!

I wanted to share with you a little site that I made: http://acmtimusru.appspot.com with two additional ranklists:

(1) countries ranklist: to compare countries between them by: rating, users, problems solved and activity = last ac; clicking on each country will get you to (2);

(2) authors by country ranklist: to compare yourself with other people from your country.

This site looks exactly like the acm.timus.ru site, with all links pointing to acm.timus.ru, except for the top red link that points to the countries ranklist.

I hope you'll find this useful. I know this site will get deprecated as soon as the admins will create these ranklists on acm.timus.ru, but I had fun building it and learning something new (google app engine).