Given an array of positive and negative numbers, arrange them in an alternate fashion such that every positive number is followed by negative and vice-versa. Order of elements in output doesn’t matter. Extra positive or negative elements should be moved to end.
Examples:
Input :
arr[] = {-2, 3, 4, -1}
Output :
arr[] = {-2, 3, -1, 4} OR {-1, 3, -2, 4} OR ..
Input :
arr[] = {-2, 3, 1}
Output :
arr[] = {-2, 3, 1} OR {-2, 1, 3}
Input :
arr[] = {-5, 3, 4, 5, -6, -2, 8, 9, -1, -4}
Output :
arr[] = {-5, 3, -2, 5, -6, 4, -4, 9, -1, 8}
OR ..We strongly recommend you to minimize your browser and try this yourself first.
We have already discussed a O(n2) solution that maintains the order of appearance in the array here. If we are allowed to change order of appearance, we can solve this problem in O(n) time and O(1) space.
The idea is to process the array and shift all negative values to the end in O(n) time. After all negative values are shifted to the end, we can easily rearrange array in alternating positive & negative items. We basically swap next positive element at even position from next negative element in this step.
Following is the implementation of above idea.
C++
// C++ program to rearrange array in alternating // positive & negative items with O(1) extra space #include <bits/stdc++.h> using namespace std;
// Function to rearrange positive and negative // integers in alternate fashion. The below // solution doesn't maintain original order of // elements void rearrange(int arr[], int n)
{ int i = -1, j = n;
// shift all negative values to the end
while (i < j)
{
while (arr[++i] > 0);
while (arr[--j] < 0);
if (i < j)
swap(arr[i], arr[j]);
}
// i has index of leftmost negative element
if (i == 0 || i == n)
return;
// start with first positive element at index 0
// Rearrange array in alternating positive &
// negative items
int k = 0;
while (k < n && i < n)
{
// swap next positive element at even position
// from next negative element.
swap(arr[k], arr[i]);
i = i + 1;
k = k + 2;
}
} // Utility function to print an array void printArray(int arr[], int n)
{ for (int i = 0; i < n; i++)
cout << arr[i] << " ";
cout << endl;
} // Driver code int main()
{ int arr[] = {2, 3, -4, -1, 6, -9};
int n = sizeof(arr)/sizeof(arr[0]);
cout << "Given array is \n";
printArray(arr, n);
rearrange(arr, n);
cout << "Rearranged array is \n";
printArray(arr, n);
return 0;
} |
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Java
//Java program to rearrange array in alternating // positive & negative items with O(1) extra space class GFG {
// Function to rearrange positive and negative // integers in alternate fashion. The below // solution doesn't maintain original order of // elements static void rearrange(int arr[], int n)
{ int i = -1, j = n;
// shift all negative values to the end
while (i < j)
{
while (arr[++i] > 0);
while (arr[--j] < 0);
if (i < j)
swap(arr, i,j);
}
// i has index of leftmost negative element
if (i == 0 || i == n)
return;
// start with first positive element at index 0
// Rearrange array in alternating positive &
// negative items
int k = 0;
while (k < n && i < n)
{
// swap next positive element at even position
// from next negative element.
swap(arr,k,i);
i = i + 1;
k = k + 2;
}
} // Utility function to print an array static void printArray(int arr[], int n)
{ for (int i = 0; i < n; i++)
System.out.print(arr[i] + " ");
System.out.println("");
} static void swap(int arr[], int index1, int index2){
int c = arr[index1];
arr[index1]=arr[index2];
arr[index2]=c;
} // Driver code public static void main(String[] args) {
int arr[] = {2, 3, -4, -1, 6, -9};
int n = arr.length;
System.out.println("Given array is ");
printArray(arr, n);
rearrange(arr, n);
System.out.println("Rearranged array is ");
printArray(arr, n);
}
} // This code is contributed by 29AjayKumar |
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Python3
# Python3 program to rearrange array # in alternating positive & negative # items with O(1) extra space # Function to rearrange positive and # negative integers in alternate fashion. # The below solution does not maintain # original order of elements def rearrange(arr, n):
i = 0
j = n - 1
# shift all negative values
# to the end
while (i < j):
while (arr[i] > 0):
i += 1
while (arr[j] < 0):
j -= 1
if (i < j):
temp = arr[i]
arr[i] = arr[j]
arr[j] = temp
# i has index of leftmost
# negative element
if (i == 0 or i == n):
return 0
# start with first positive element
# at index 0
# Rearrange array in alternating
# positive & negative items
k = 0
while (k < n and i < n):
# swap next positive element at even
# position from next negative element.
temp = arr[k]
arr[k] = arr[i]
arr[i] = temp
i = i + 1
k = k + 2
# Utility function to print an array def printArray(arr, n):
for i in range(n):
print(arr[i], end = " ")
print("\n")
# Driver code arr = [2, 3, -4, -1, 6, -9]
n = len(arr)
print( "Given array is")
printArray(arr, n) rearrange(arr, n) print( "Rearranged array is")
printArray(arr, n) # This code is contributed # Princi Singh |
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C#
// C# program to rearrange array // in alternating positive & negative // items with O(1) extra space using System;
class GFG
{ // Function to rearrange positive and // negative integers in alternate fashion. // The below solution doesn't maintain // original order of elements static void rearrange(int []arr, int n)
{ int i = -1, j = n;
// shift all negative values
// to the end
while (i < j)
{
while (arr[++i] > 0);
while (arr[--j] < 0);
if (i < j)
swap(arr, i,j);
}
// i has index of leftmost
// negative element
if (i == 0 || i == n)
return;
// start with first positive
// element at index 0
// Rearrange array in alternating
// positive & negative items
int k = 0;
while (k < n && i < n)
{
// swap next positive element
// at even position from next
// negative element.
swap(arr, k, i);
i = i + 1;
k = k + 2;
}
} // Utility function to print an array static void printArray(int []arr, int n)
{ for (int i = 0; i < n; i++)
Console.Write(arr[i] + " ");
Console.WriteLine("");
} static void swap(int []arr, int index1,
int index2)
{ int c = arr[index1];
arr[index1] = arr[index2];
arr[index2] = c;
} // Driver code public static void Main()
{ int []arr = {2, 3, -4, -1, 6, -9};
int n = arr.Length;
Console.WriteLine("Given array is ");
printArray(arr, n);
rearrange(arr, n);
Console.WriteLine("Rearranged array is ");
printArray(arr, n);
} } // This code is contributed // by 29AjayKumar |
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PHP
<?php // PHP program to rearrange array // in alternating positive & negative // items with O(1) extra space // Function to rearrange positive and // negative integers in alternate fashion. // The below solution doesn't maintain // original order of elements function rearrange(&$arr, $n)
{ $i = -1;
$j = $n;
// shift all negative values
// to the end
while ($i < $j)
{
while ($arr[++$i] > 0);
while ($arr[--$j] < 0);
if ($i < $j)
{
$temp = $arr[$i];
$arr[$i] = $arr[$j];
$arr[$j] = $temp;
}
}
// i has index of leftmost
// negative element
if ($i == 0 || $i == $n)
return;
// start with first positive element
// at index 0
// Rearrange array in alternating
// positive & negative items
$k = 0;
while ($k < $n && $i < $n)
{
// swap next positive element at even
// position from next negative element.
$temp = $arr[$k];
$arr[$k] = $arr[$i];
$arr[$i] = $temp;
$i = $i + 1;
$k = $k + 2;
}
} // Utility function to print an array function printArray(&$arr, $n)
{ for ($i = 0; $i < $n; $i++)
echo $arr[$i] . " ";
echo "\n";
} // Driver code $arr = array(2, 3, -4, -1, 6, -9);
$n = sizeof($arr);
echo "Given array is \n";
printArray($arr, $n);
rearrange($arr, $n);
echo "Rearranged array is \n";
printArray($arr, $n);
// This code is contributed // by ChitraNayal ?> |
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Output:
Given array is 2 3 -4 -1 6 -9 Rearranged array is -1 3 -4 2 -9 6
This article is contributed by Aditya Goel. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above
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