Type like pro

First increasing second decreasing tuple

Problem

Given N pairs of integers, write an algorithm to sort the pairs so that the first number in each pair is sorted increasingly while the second number in each pair is sorted decreasingly. The first and second numbers in each pair can be swapped. Sometimes there will be no solution, in that case return an error.

Examples:
*
* Input: 1 5 7 1 3 8 5 6
*
* Output: 1 7 <- Swapped 1 5 6 5 <- Swapped 8 3 <- Swapped
*
* Input: 1 5 6 9
*
* Output: Not Possible

Solution

This is solved by backtracking. In a loop we try to put each tuple at the beginning and then try to put the consecutive tuples following the constraint, that first number will be increasing and second number will be decreasing. Every tuple is tried two ways one with the given tuple and another one is with reversed. If we can put a tuple following the constraint we call the recursive function with the rest of the tuples, If we cannot put a tuple we try with the next tuple. If no tuple can be put at that location we backtrack and try with another tuple in the previous location. If we are able to put the tuple when there is only one tuple left, then we found a solution. If we backtrack to the first element and could not find a solution after trying with all tuples, then we return the error that no arrangement possible.

Code

```import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class IncreasingDecreasingTuple
{
static int count = 0;

/**
* Given N pairs of integers, write an algorithm to sort
* the pairs so that the first number in each pair is sorted
* increasingly while the second number in each pair is sorted
* decreasingly. The first and second numbers in each pair
* can be swapped. Sometimes there will be no solution,
* in that case return an error.
*
* Examples:
*
* Input: 1 5 7 1 3 8 5 6
*
* Output:
* 1 7  < - Swapped 1 5 6 5  < - Swapped 8 3  < - Swapped
*
* Input: 1 5 6 9
*
* Output: Not Possible
*
* @param args
*/
public static void main(String[] args)
{
Integer[][] input =
{
{ 1, 5 },
{ 7, 1 },
{ 3, 8 },
{ 5, 6 } };
List < List < Integer >  >  list =
new ArrayList < List < Integer >  > ();
for (Integer[] tuple : input)
{
List < Integer >  tupleList =
new ArrayList < Integer > ();
for (Integer el : tuple)
{
}
}

System.out.println(getArrangeMent(list));

}

public static List < List < List < Integer >  >  >
getArrangeMent(List < List < Integer >  >  list)
{
List < List < List < Integer >  >  >  result =
new ArrayList < List < List < Integer >  >  > ();
for (int i = 0; i  <  list.size(); ++i)
{
List < Integer >  tuple = list.get(i);
List < List < Integer >  >  subList =
new ArrayList < List < Integer >  > (list);
subList.remove(i);
List < List < List < Integer >  >  >  r1 =
getRecurseArrangeMent(tuple, subList);
if (r1 != null)
List < Integer >  rTuple = new ArrayList < Integer > (tuple);
Collections.reverse(rTuple);
List < List < List < Integer >  >  >  r2 =
getRecurseArrangeMent(rTuple, subList);
if (r2 != null)
}
return result;
}

public static List < List < List < Integer >  >  >
getRecurseArrangeMent(
List < Integer >  start, List < List < Integer >  >  list)
{
List < List < List < Integer >  >  >  result =
new ArrayList < List < List < Integer >  >  > ();
if (list.size() == 0)
return result;

for (int i = 0; i  <  list.size(); ++i)
{
List < Integer >  tuple = list.get(i);
if (tuple.get(0)  >= start.get(0) && start.get(1)  >=
tuple.get(1))
{
List < List < Integer >  >  subList =
new ArrayList < List < Integer >  > (list);
subList.remove(i);
List < List < List < Integer >  >  >  r1 =
getRecurseArrangeMent(tuple, subList);
if (r1 != null)
}
List < Integer >  rTuple = new ArrayList < Integer > (tuple);
Collections.reverse(rTuple);
if (rTuple.get(0)  >= start.get(0) && start.get(1)  >=
rTuple.get(1))
{
List < List < Integer >  >  subList =
new ArrayList < List < Integer >  > (list);
subList.remove(i);
List < List < List < Integer >  >  >  r1 =
getRecurseArrangeMent(rTuple, subList);
if (r1 != null)
}
}
if (result.size() != 0)
return result;
return null;
}

public static List < List < List < Integer >  >  >
prepend(List < Integer >  start,
List < List < List < Integer >  >  >  list)
{
List < List < List < Integer >  >  >  results =
new ArrayList < List < List < Integer >  >  > ();
if (list.size() == 0)
{
List < List < Integer >  >  result =
new ArrayList < List < Integer >  > ();
} else
{
for (List < List < Integer >  >  result : list)
{