Move all zeros to start and ones to end in an Array of random integers

Given an array arr[] of random integers, the task is to push all the zero’s in the array to the start and all the one’s to the end of the array. Note that the order of all the other elements should be the same.

Example:

Input: arr[] = {1, 2, 0, 4, 3, 0, 5, 0}
Output: 0 0 0 2 4 3 5 1

Input: arr[] = {1, 2, 0, 0, 0, 3, 6};
Output: 0 0 0 2 3 6 1



Approach: Traverse the array from left to right and move all the elements which are not equal to 1 at the beginning and then put 1’s in the rest of the indices at the end of the array. Now, find the index of the last element which is not equal to 1 say lastInd and then starting from this index to the beginning of the array push all the elements which are not equal to 0 in the end till lastInd and then put 0’s in the beginning.

Below is the implementation of the above approach:

C++

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// C++ implementation of the approach
#include <iostream>
using namespace std;
  
// Utility function to print
// the contenets of an array
void printArr(int arr[], int n)
{
    for (int i = 0; i < n; i++)
        cout << arr[i] << " ";
}
  
// Function that pushes all the zeros
// to the start and ones to the end of an array
void pushBinaryToBorder(int arr[], int n)
{
  
    // To store the count of elements
    // which are not equal to 1
    int count1 = 0;
  
    // Traverse the array and calculate
    // count of elements which are not 1
    for (int i = 0; i < n; i++)
        if (arr[i] != 1)
            arr[count1++] = arr[i];
  
    // Now all non-ones elements have been shifted to
    // front and 'count1' is set as index of first 1.
    // Make all elements 1 from count to end.
    while (count1 < n)
        arr[count1++] = 1;
  
    // Initialize lastNonBinary position to zero
    int lastNonOne = 0;
  
    // Traverse the array and pull non-zero
    // elements to the required indices
    for (int i = n - 1; i >= 0; i--) {
  
        // Ignore the 1's
        if (arr[i] == 1)
            continue;
        if (!lastNonOne) {
  
            // Mark the position Of
            // last NonBinary integer
            lastNonOne = i;
        }
  
        // Place non-zero element to
        // their required indices
        if (arr[i] != 0)
            arr[lastNonOne--] = arr[i];
    }
  
    // Put zeros to start of array
    while (lastNonOne >= 0)
        arr[lastNonOne--] = 0;
}
  
// Driver code
int main()
{
    int arr[] = { 1, 2, 0, 0, 0, 3, 6 };
    int n = sizeof(arr) / sizeof(arr[0]);
    pushBinaryToBorder(arr, n);
    printArr(arr, n);
  
    return 0;
}

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Java

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// Java implementation of the approach
import java.util.*;
  
class GFG
{
  
// Utility function to print
// the contenets of an array
static void printArr(int arr[], int n)
{
    for (int i = 0; i < n; i++)
        System.out.print(arr[i]+" ");
}
  
// Function that pushes all the zeros
// to the start and ones to the end of an array
static void pushBinaryToBorder(int arr[], int n)
{
  
    // To store the count of elements
    // which are not equal to 1
    int count1 = 0;
  
    // Traverse the array and calculate
    // count of elements which are not 1
    for (int i = 0; i < n; i++)
        if (arr[i] != 1)
            arr[count1++] = arr[i];
  
    // Now all non-ones elements have been shifted to
    // front and 'count1' is set as index of first 1.
    // Make all elements 1 from count to end.
    while (count1 < n)
        arr[count1++] = 1;
  
    // Initialize lastNonBinary position to zero
    int lastNonOne = 0;
  
    // Traverse the array and pull non-zero
    // elements to the required indices
    for (int i = n - 1; i >= 0; i--) 
    {
  
        // Ignore the 1's
        if (arr[i] == 1)
            continue;
        if (lastNonOne == 0)
        {
  
            // Mark the position Of
            // last NonBinary integer
            lastNonOne = i;
        }
  
        // Place non-zero element to
        // their required indices
        if (arr[i] != 0)
            arr[lastNonOne--] = arr[i];
    }
  
    // Put zeros to start of array
    while (lastNonOne >= 0)
        arr[lastNonOne--] = 0;
}
  
// Driver code
public static void main(String args[])
{
    int arr[] = { 1, 2, 0, 0, 0, 3, 6 };
    int n = arr.length;
    pushBinaryToBorder(arr, n);
    printArr(arr, n);
  
}
}
  
// This code is contributed by SURENDRA_GANGWAR.

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Python3

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# Python3 implementation of the approach 
  
# Utility function to print 
# the contenets of an array 
def printArr(arr, n) : 
  
    for i in range(n) :
        print(arr[i],end=" "
  
  
# Function that pushes all the zeros 
# to the start and ones to the end of an array 
def pushBinaryToBorder(arr, n) : 
  
    # To store the count of elements 
    # which are not equal to 1 
    count1 = 0
      
    # Traverse the array and calculate 
    # count of elements which are not 1 
    for i in range(n) :
        if (arr[i] != 1) :
            arr[count1] = arr[i]
            count1 += 1
  
    # Now all non-ones elements have been shifted to 
    # front and 'count1' is set as index of first 1. 
    # Make all elements 1 from count to end. 
    while (count1 < n) :
        arr[count1] = 1
        count1 += 1
  
    # Initialize lastNonBinary position to zero 
    lastNonOne = 0
  
    # Traverse the array and pull non-zero 
    # elements to the required indices 
    for i in range(n - 1, -1, -1) :
  
        # Ignore the 1's 
        if (arr[i] == 1) : 
            continue
              
        if (not lastNonOne) :
  
            # Mark the position Of 
            # last NonBinary integer 
            lastNonOne = i
  
        # Place non-zero element to 
        # their required indices 
        if (arr[i] != 0) :
            arr[lastNonOne] = arr[i]
            lastNonOne -= 1
  
    # Put zeros to start of array 
    while (lastNonOne >= 0) :
        arr[lastNonOne] = 0
        lastNonOne -= 1
  
# Driver code 
if __name__ == "__main__" :
      
    arr = [ 1, 2, 0, 0, 0, 3, 6 ]; 
    n = len(arr); 
    pushBinaryToBorder(arr, n) 
    printArr(arr, n)
  
# This code is contributed by Ryuga

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Output:

0 0 0 2 3 6 1


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