static void Main(string[] args)
{
string input;
int i = 0;
Translator[] translators = new Translator[0];
int hiredTranslators = 0;
int languagesSpoken = 0;
while ((input = Console.ReadLine()) != null)
{
var split = input.Split();
if (hiredTranslators == 0)
{
languagesSpoken = int.Parse(split[0]);
hiredTranslators = int.Parse(split[1]);
if (hiredTranslators % 2 != 0)
{
Console.WriteLine("impossible"); return;
}
translators = new Translator[hiredTranslators];
}
else
{
translators[i] = new Translator
{
ID = i,
FirstLanguage = int.Parse(split[0]),
SecondLanguage = int.Parse(split[1])
};
i++;
}
}
var matchArr = new List <TranslatorPair>();
for (int j = 0; j < hiredTranslators; j++)
{
for (int k = 0; k < hiredTranslators; k++)
{
if (translators[j].FirstLanguage == translators[k].FirstLanguage)
{
matchArr.Add(new TranslatorPair {
Left = translators[j].ID, Right = translators[k].ID
});
}
else if (translators[j].FirstLanguage == translators[k].SecondLanguage)
{
matchArr.Add(new TranslatorPair {
Left = translators[j].ID, Right = translators[k].ID
});
}
else if (translators[j].SecondLanguage == translators[k].SecondLanguage)
{
matchArr.Add(new TranslatorPair {
Left = translators[j].ID, Right = translators[k].ID
});
}
else if (translators[j].SecondLanguage == translators[k].FirstLanguage)
{
matchArr.Add(new TranslatorPair {
Left = translators[j].ID, Right = translators[k].ID
});
}
}
}
matchArr = matchArr.Where(x => x.Left != x.Right).ToList();
for (int z = 0; z < matchArr.Count; z++)
{
for (int x = 0; x < matchArr.Count; x++)
{
if (matchArr[z].Left == matchArr[x].Right && matchArr[z].Right == matchArr[x].Left)
{
matchArr.Remove(matchArr[z]);
}
}
}
var tmpListMatches = matchArr.ToList();
if (matchArr.Count == 0)
{
throw new Exception();
}
var tmpArray = new TranslatorPair[hiredTranslators / 2];
var index = 0;
var rnd = new Random();
var triedCombos = new List <TranslatorPair>();
var tmpTest = new TranslatorPair();
var result = new List <TranslatorPair>();
var tmpBranch = new List <List <TranslatorPair> >();
for (int l = 0; result.Count != hiredTranslators / 2; l++)
{
//if (l >= tmpArray.Length)
//{
// tmpListMatches = matchArr.ToList();
// l = 0;
// index++;
//}
//if (tmpListMatches.Count == 0)
//{
// l = 0;
// index++;
//}
//if (l == 0)
// tmpArray[0] = tmpTest = tmpListMatches[index];
//else
// tmpArray[l] = tmpTest = tmpListMatches[rnd.Next(0, tmpListMatches.Count)];
//tmpListMatches = tmpListMatches.FindAll(x => x.Left != tmpTest.Left && x.Left != tmpTest.Right && x.Right != tmpTest.Left && x.Right != tmpTest.Right);
//IGraph myGraph = (IGraph)matchArr.ToList();
//TranslatorPair start = matchArr[index];
//var result = myGraph.DepthFirstTraversal(start)
// .Where(x => x.Left != tmpArray[l].Left && x.Left != tmpArray[l].Right && x.Right != tmpArray[l].Left && x.Right != tmpArray[l].Right)
// .FirstOrDefault();
//tmpArray[l] = result;
//TranslatorPair result = myGraph.DepthFirstTraversal(start)
// .Where(x => x.Left != start.Left && x.Left != start.Right && x.Right != start.Left && x.Right != start.Right)
// .FirstOrDefault();
result = TraverseDepthFirst(matchArr[l], GetPairs).ToList();
}
foreach (var item in result)
{
Console.WriteLine($"{item.Left} {item.Right}");
}
//for (int i1 = 0; i1 < tmpArray.Length; i1++)
//{
// var item = tmpArray[i1];
// if (item != null)
// Console.WriteLine($"{item.Left} {item.Right}");
//}
IEnumerable <TranslatorPair> GetPairs(TranslatorPair arg, int level)
{
if (level == 0 && tmpBranch.Count != 0)
{
return(tmpBranch[level].First(x => x.Left != arg.Left && x.Left != arg.Right && x.Right != arg.Left && x.Right != arg.Right));
}
if (level == 0)
{
tmpBranch.Add(tmpListMatches.First(x => x.Left != arg.Left && x.Left != arg.Right && x.Right != arg.Left && x.Right != arg.Right));
}
else
{
tmpBranch.Add(tmpBranch[level - 1].First(x => x.Left != arg.Left && x.Left != arg.Right && x.Right != arg.Left && x.Right != arg.Right));
}
return(tmpBranch[level]);
//tmpListMatches = tmpListMatches.FindAll(x => x.Left != arg.Left && x.Left != arg.Right && x.Right != arg.Left && x.Right != arg.Right);
//return tmpListMatches.FindAll(x => x.Left != arg.Left && x.Left != arg.Right && x.Right != arg.Left && x.Right != arg.Right);
//return tmpListMatches;
}
}
static void Main(string[] args)
{
string input;
int i = 0;
Translator[] translators = new Translator[0];
int hiredTranslators = 0;
int languagesSpoken = 0;
while ((input = Console.ReadLine()) != null)
{
var split = input.Split();
if (hiredTranslators == 0)
{
languagesSpoken = int.Parse(split[0]);
hiredTranslators = int.Parse(split[1]);
if (hiredTranslators % 2 != 0)
{
Console.WriteLine("impossible"); return;
}
translators = new Translator[hiredTranslators];
}
else
{
translators[i] = new Translator
{
ID = i,
FirstLanguage = int.Parse(split[0]),
SecondLanguage = int.Parse(split[1])
};
i++;
}
}
var matchArr = new List <TranslatorPair>();
for (int j = 0; j < hiredTranslators; j++)
{
//if (!(matchArr[j].Left == translatorArray[j].ID && matchArr[j].Right == translatorArray[j].ID))
for (int k = 0; k < hiredTranslators; k++)
{
//matchArr.Add(new TranslatorPair { Left = translators[j].ID, Right = translators[k].ID });
//if (!matchArr.Any(x => x.Left + x.Right == matchArr[j].Left + matchArr[k].Right))
if (translators[j].FirstLanguage == translators[k].FirstLanguage)
{
matchArr.Add(new TranslatorPair {
Left = translators[j].ID, Right = translators[k].ID
});
}
else if (translators[j].FirstLanguage == translators[k].SecondLanguage)
{
matchArr.Add(new TranslatorPair {
Left = translators[j].ID, Right = translators[k].ID
});
}
else if (translators[j].SecondLanguage == translators[k].SecondLanguage)
{
matchArr.Add(new TranslatorPair {
Left = translators[j].ID, Right = translators[k].ID
});
}
else if (translators[j].SecondLanguage == translators[k].FirstLanguage)
{
matchArr.Add(new TranslatorPair {
Left = translators[j].ID, Right = translators[k].ID
});
}
}
}
matchArr = matchArr.Where(x => x.Left != x.Right).ToList();
//var tmpListMatches = new List<TranslatorPair>();
for (int z = 0; z < matchArr.Count; z++)
{
//if (matchArr.Any(x => matchArr[z].Left == x.Right && matchArr[z].Right == x.Left))
// matchArr.Remove(matchArr[z]);
//tmpListMatches.Add(matchArr.First(x => x.Left + x.Right == matchArr[z].Left + matchArr[z].Right));
for (int x = 0; x < matchArr.Count; x++)
{
if (matchArr[z].Left == matchArr[x].Right && matchArr[z].Right == matchArr[x].Left)
{
matchArr.Remove(matchArr[z]);
}
//if (matchArr[z].Left + matchArr[z].Right == matchArr[x].Left + matchArr[x].Right)
// tmpListMatches.Add(matchArr[z]);
}
//tmpListMatches.Add(matchArr.First(x => x.Left + x.Left == matchArr[z].Left + matchArr[z].Right));
//tmpListMatches = matchArr.Where(x => x.Left + x.Right != matchArr[z].Left + matchArr[z].Right).ToList();
}
//if (matchArr.Count > 4000)
// Console.WriteLine("impossible");
//var tmpListMatches = new Queue<TranslatorPair>(matchArr);
var tmpListMatches = matchArr.ToList();
if (matchArr.Count == 0)
{
throw new Exception();
}
var tmpArray = new TranslatorPair[hiredTranslators / 2];
var index = 0;
var rnd = new Random();
var triedCombos = new List <TranslatorPair>();
//for (int l = 0; tmpArray.Any(x => x == null) /*&& l < tmpArray.Length*/; l++)
//{
// if (tmpListMatches.Count == 0)
// {
// tmpListMatches = matchArr.ToList();
// for (int m = 1; m < tmpArray.Length; m++)
// {
// tmpArray[m] = null;
// }
// tmpListMatches.RemoveAll(x => x.Left == tmpArray[0].Left || x.Right == tmpArray[0].Right || x.Left == tmpArray[0].Right || x.Right == tmpArray[0].Left);
// tmpListMatches = tmpListMatches.Except(triedCombos).ToList();
// l = 1;
// if (tmpListMatches.Count == 0)
// {
// tmpListMatches = matchArr.ToList();
// triedCombos.Clear();
// l = 0;
// index++;
// }
// }
// if (l == 0)
// tmpArray[l] = tmpListMatches[index];
// else
// {
// tmpArray[l] = tmpListMatches[0];
// //tmpArray[l] = tmpListMatches[rnd.Next(0, tmpListMatches.Count)];
// triedCombos.Add(tmpArray[l]);
// }
// tmpListMatches.RemoveAll(x => x.Left == tmpArray[l].Left || x.Right == tmpArray[l].Right || x.Left == tmpArray[l].Right || x.Right == tmpArray[l].Left);
//}
//var testArr = matchArr.GroupBy(x => x.Right);
//var testArr2 = matchArr.GroupBy(x => x.Left).OrderByDescending(x => x.Key).ToList();
var tmpTest = new TranslatorPair();
//matchArr.OrderByDescending(x => x.Right);
for (int l = 0; l < tmpArray.Length; l++)
{
if (tmpListMatches.Count == 0)
{
tmpListMatches = matchArr.ToList();
l = 0;
index++;
if (index >= tmpListMatches.Count)
{
index = 0;
}
//if (languagesSpoken > 99)
// throw new Exception();
}
if (l == 0)
{
//try
//{
// tmpArray[0] = tmpTest = tmpListMatches[index];
//}
//catch (Exception)
//{
// if (index > tmpListMatches.Count - 1)
// Console.WriteLine("impossible");
// if (tmpArray[0] == null)
// throw new Exception();
// Environment.Exit(0);
//}
tmpArray[0] = tmpTest = tmpListMatches[index];
}
else
{
//tmpArray[l] = tmpTest = tmpListMatches[0];
tmpArray[l] = tmpTest = tmpListMatches[rnd.Next(0, tmpListMatches.Count)];
}
tmpListMatches = tmpListMatches.FindAll(x => x.Left != tmpTest.Left && x.Left != tmpTest.Right && x.Right != tmpTest.Left && x.Right != tmpTest.Right);
tmpListMatches = tmpListMatches.FindAll(x => x.Left != tmpTest.Left && x.Left != tmpTest.Right && x.Right != tmpTest.Left && x.Right != tmpTest.Right);
}
for (int i1 = 0; i1 < tmpArray.Length; i1++)
{
var item = tmpArray[i1];
if (item != null)
{
Console.WriteLine($"{item.Left} {item.Right}");
}
}
}