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Segregating negative and positive maintaining order and O(1) space
  • Difficulty Level : Medium
  • Last Updated : 21 Aug, 2018

Segregation of negative and positive numbers in an array without using extra space, and maintaining insertion order and in O(n) time complexity.

Examples:

Input :9
       12 11 -13 -5 6 -7 5 -3 -6
Output :-13 -5 -7 -3 -6 12 11 6 5 

Input :5
       11 -13 6 -7 5
Output :-13 -7 11 6 5

We have discussed this problem in below posts.

  1. ers-beginning-positive-end-constant-extra-space/”>Rearrange positive and negative numbers without maintaining order.
  2. Rearrange positive and negative numbers with constant extra space

In this post a new approach is discussed that takes O(1) extra space. We firs count total negative numbers, then move negative numbers one by one to correct position.

C++

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// C++ program to move all negative numbers
// to beginning and positive numbers to end
// keeping order.
#include <iostream>
using namespace std;
  
void segregate(int arr[], int n)
{
    // Count negative numbers
    int count_negative = 0;
    for (int i = 0; i < n; i++) 
        if (arr[i] < 0)
            count_negative++;    
  
    // Run a loop until all negative
    // numbers are moved to the beginning
    int i = 0, j = i + 1;
    while (i != count_negative) {
  
        // If number is negative, update
        // position of next positive number.
        if (arr[i] < 0) {
            i++;
            j = i + 1;
        }
  
        // If number is positive, move it to
        // index j and increment j.
        else if (arr[i] > 0 && j < n) {
            swap(arr[i], arr[j]);
            j++;
        }
    }
}
  
int main()
{
    int count_negative = 0;
    int arr[] = { -12, 11, -13, -5, 6, -7, 5, -3, -6 };
    int n = sizeof(arr) / sizeof(arr[0]);
    segregate(arr, n);
    for (int i = 0; i < n; i++)
        cout << arr[i] << " "
}

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Java

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// Java program to move all 
// negative numbers to beginning 
// and positive numbers to end
// keeping order.
class GFG
{
static void segregate(int arr[], 
                      int n)
{
      
// Count negative numbers
int count_negative = 0;
for (int i = 0; i < n; i++) 
    if (arr[i] < 0)
        count_negative++; 
  
// Run a loop until all 
// negative numbers are 
// moved to the beginning
int i = 0, j = i + 1;
while (i != count_negative)
{
  
    // If number is negative, 
    // update position of next
    // positive number.
    if (arr[i] < 0
    {
        i++;
        j = i + 1;
    }
  
    // If number is positive, move 
    // it to index j and increment j.
    else if (arr[i] > 0 && j < n) 
    {
        int t = arr[i];
        arr[i] = arr[j];
        arr[j] = t;
        j++;
    }
}
}
  
// Driver code
public static void main(String[] args) 
{
    int count_negative = 0;
    int arr[] = { -12, 11, -13, -5,
                   6, -7, 5, -3, -6 };
    int n = arr.length;
    segregate(arr, n);
    for (int i = 0; i < n; i++)
        System.out.print(arr[i] + " "); 
}
  
// This code is contributed 
// by ChitraNayal

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C#

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// C# program to move all 
// negative numbers to beginning
// and positive numbers to end
// keeping order.
using System;
  
class GFG
{
static void segregate(int[] arr, 
                      int n)
{
      
// Count negative numbers
int count_negative = 0,i;
for (i = 0; i < n; i++) 
    if (arr[i] < 0)
        count_negative++; 
  
// Run a loop until all 
// negative numbers are
// moved to the beginning
i = 0;
int j = i + 1;
while (i != count_negative) 
{
  
    // If number is negative, 
    // update position of next 
    // positive number.
    if (arr[i] < 0) 
    {
        i++;
        j = i + 1;
    }
  
    // If number is positive, move 
    // it to index j and increment j.
    else if (arr[i] > 0 && j < n)
    {
        int t = arr[i];
        arr[i] = arr[j];
        arr[j] = t;
        j++;
    }
}
}
  
// Driver code
public static void Main() 
{
    int[] arr = { -12, 11, -13, -5, 
                    6, -7, 5, -3, -6 };
    int n = arr.Length;
    segregate(arr, n);
    for (int i = 0; i < n; i++)
        Console.Write(arr[i] + " "); 
}
  
// This code is contributed 
// by ChitraNayal

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Python 3

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# Python 3 program to move all 
# negative numbers to beginning
# and positive numbers to end
# keeping order.
  
def segregate(arr, n):
      
    # Count negative numbers
    count_negative = 0
    for i in range(n): 
        if (arr[i] < 0):
            count_negative += 1
  
    # Run a loop until all 
    # negative numbers are 
    # moved to the beginning
    i = 0
    j = i + 1
    while (i != count_negative):
  
        # If number is negative, 
        # update position of next 
        # positive number.
        if (arr[i] < 0) :
            i += 1
            j = i + 1
  
        # If number is positive, move 
        # it to index j and increment j.
        elif (arr[i] > 0 and j < n):
            t = arr[i]
            arr[i] = arr[j]
            arr[j] = t
            j += 1
          
# Driver Code
count_negative = 0
arr = [-12, 11, -13, -5
        6, -7, 5, -3, -6 ]
segregate(arr, 9)
for i in range(9):
    print(arr[i] , end =" ")
  
# This code is contributed
# by ChitraNayal

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PHP

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<?php 
// PHP program to move all 
// negative numbers to 
// beginning and positive 
// numbers to end keeping order.
  
function segregate(&$arr, $n)
{
    // Count negative numbers
    $count_negative = 0;
    for ($i = 0; $i < $n; $i++) 
        if ($arr[$i] < 0)
            $count_negative++; 
  
    // Run a loop until all 
    // negative numbers are
    // moved to the beginning
    $i = 0;
    $j = $i + 1;
    while ($i != $count_negative)
    {
  
        // If number is negative, 
        // update position of next
        // positive number.
        if ($arr[$i] < 0) 
        {
            $i++;
            $j = $i + 1;
        }
  
        // If number is positive, move 
        // it to index j and increment j.
        else if ($arr[$i] > 0 && $j < $n)
        {
            $t = $arr[$i];
            $arr[$i] = $arr[$j];
            $arr[$j] = $t;
            $j++;
        }
    }
}
  
// Driver Code
$count_negative = 0;
$arr = array(-12, 11, -13, -5, 
              6, -7, 5, -3, -6);
$n = sizeof($arr);
segregate($arr, $n);
for ($i = 0; $i < $n; $i++)
    echo $arr[$i] ." "
      
// This code is contributed
// by ChitraNayal
?>

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Output:

-12 -13 -5 -7 -3 -6 11 6 5 

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