Move all negative numbers to beginning and positive to end with constant extra space

An array contains both positive and negative numbers in random order. Rearrange the array elements so that all negative numbers appear before all positive numbers.

Examples :

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

Note :- Order of elements is not important here.

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

The idea is to simply apply partition process of quicksort.

C++

// A C++ program to put all negative 
// numbers before positive numbers 
#include <bits/stdc++.h> 
using namespace std; 
  
void rearrange(int arr[], int n) 
{ 
    int j = 0; 
    for (int i = 0; i < n; i++) { 
        if (arr[i] < 0) { 
            if (i != j) 
                swap(arr[i], arr[j]); 
            j++; 
        } 
    } 
} 
  
// A utility function to print an array 
void printArray(int arr[], int n) 
{ 
    for (int i = 0; i < n; i++) 
        printf("%d ", arr[i]); 
} 
  
// Driver code 
int main() 
{ 
    int arr[] = { -1, 2, -3, 4, 5, 6, -7, 8, 9 }; 
    int n = sizeof(arr) / sizeof(arr[0]); 
    rearrange(arr, n); 
    printArray(arr, n); 
    return 0; 
} 

Java

// Java program to put all negative 
// numbers before positive numbers 
import java.io.*; 
  
class GFG { 
  
    static void rearrange(int arr[], int n) 
    { 
        int j = 0, temp; 
        for (int i = 0; i < n; i++) { 
            if (arr[i] < 0) { 
                if (i != j) { 
                    temp = arr[i]; 
                    arr[i] = arr[j]; 
                    arr[j] = temp; 
                } 
                j++; 
            } 
        } 
    } 
  
    // A 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] + " "); 
    } 
  
    // Driver code 
    public static void main(String args[]) 
    { 
        int arr[] = { -1, 2, -3, 4, 5, 6, -7, 8, 9 }; 
        int n = arr.length; 
  
        rearrange(arr, n); 
        printArray(arr, n); 
    } 
} 
  
// This code is contributed by Nikita Tiwari. 

Python3

# A Python 3 program to put 
# all negative numbers before 
# positive numbers 
  
def rearrange(arr, n ) : 
  
    # Please refer partition() in  
    # below post 
    # https://www.geeksforgeeks.org / quick-sort / j = 0 
    j = 0 
    for i in range(0, n) : 
        if (arr[i] < 0) : 
            temp = arr[i] 
            arr[i] = arr[j] 
            arr[j]= temp 
            j = j + 1
    print(arr) 
  
# Driver code 
arr = [-1, 2, -3, 4, 5, 6, -7, 8, 9] 
n = len(arr) 
rearrange(arr, n) 
  
  
# This code is contributed by Nikita Tiwari. 

C#

// C# program to put all negative 
// numbers before positive numbers 
using System; 
  
class GFG { 
    static void rearrange(int[] arr, int n) 
    { 
  
        int j = 0, temp; 
        for (int i = 0; i < n; i++) { 
            if (arr[i] < 0) { 
                temp = arr[i]; 
                arr[i] = arr[j]; 
                arr[j] = temp; 
                j++; 
            } 
        } 
    } 
  
    // A utility function to print an array 
    static void printArray(int[] arr, int n) 
    { 
        for (int i = 0; i < n; i++) 
            Console.Write(arr[i] + " "); 
    } 
  
    // Driver code 
    public static void Main() 
    { 
        int[] arr = { -1, 2, -3, 4, 5, 6, -7, 8, 9 }; 
        int n = arr.Length; 
  
        rearrange(arr, n); 
        printArray(arr, n); 
    } 
} 
  
// This code is contributed by nitin mittal. 

PHP

<?php  
// A PHP program to put all negative 
// numbers before positive numbers 
  
function rearrange(&$arr, $n) 
{ 
    $j = 0; 
    for ($i = 0; $i < $n; $i++) 
    { 
        if ($arr[$i] < 0)  
        { 
            if ($i != $j) 
            { 
                $temp = $arr[$i]; 
                $arr[$i] = $arr[$j]; 
                $arr[$j] = $temp; 
            } 
            $j++; 
        } 
    } 
} 
  
// A utility function to print an array 
function printArray(&$arr, $n) 
{ 
    for ($i = 0; $i < $n; $i++) 
        echo $arr[$i]." "; 
} 
  
// Driver code 
$arr = array(-1, 2, -3, 4, 5, 6, -7, 8, 9 ); 
$n = sizeof($arr); 
rearrange($arr, $n); 
printArray($arr, $n); 
  
// This code is contributed by ChitraNayal 
?> 

Output:

 -1 -3 -7 4 5 6 2 8 9

Time complexity: O(n)
Auxiliary Space: O(1)

The problem becomes difficult if we need to maintain order of elements. Please refer Rearrange positive and negative numbers with constant extra space for details.

This article is contributed by Apoorva. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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Recommended: Please try your approach on {IDE} first, before moving on to the solution.

C++

Java

Python3

C#

PHP

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