Sort an array of 0s, 1s and 2s (Simple Counting) (original) (raw)

Last Updated : 17 Jan, 2024

Given an array A[] consisting of 0s, 1s, and 2s, write a function that sorts A[]. The functions should put all 0s first, then all 1s, and all 2s in last.

Examples:

**Input: {0, 1, 2, 0, 1, 2}
**Output: {0, 0, 1, 1, 2, 2}

**Input: {0, 1, 1, 0, 1, 2, 1, 2, 0, 0, 0, 1}
**Output: {0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 2, 2}

Count the number of 0's, 1's, and 2's. After Counting, put all 0's first, then 1's and lastly 2's in the array. We traverse the array two times.

C++ `

// Simple C++ program to sort an array of 0s 1s and 2s. #include using namespace std;

void sort012(int* arr, int n) { // Variables to maintain the count of 0's, 1's and 2's // in the array int count0 = 0, count1 = 0, count2 = 0; for (int i = 0; i < n; i++) { if (arr[i] == 0) count0++; if (arr[i] == 1) count1++; if (arr[i] == 2) count2++; }

// Putting the 0's in the array in starting.
for (int i = 0; i < count0; i++)
    arr[i] = 0;

// Putting the 1's in the array after the 0's.
for (int i = count0; i < (count0 + count1); i++)
    arr[i] = 1;

// Putting the 2's in the array after the 1's
for (int i = (count0 + count1); i < n; i++)
    arr[i] = 2;

return;

}

// Prints the 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[] = { 0, 1, 1, 0, 1, 2, 1, 2, 0, 0, 0, 1 }; int n = sizeof(arr) / sizeof(arr[0]); sort012(arr, n); printArray(arr, n); return 0; }

// This code is contributed by Aditya Kumar (adityakumar129)

C

// Simple C program to sort an array of 0s 1s and 2s. #include <stdio.h>

void sort012(int* arr, int n) { // Variables to maintain the count of 0's, 1's and 2's // in the array int count0 = 0, count1 = 0, count2 = 0; for (int i = 0; i < n; i++) { if (arr[i] == 0) count0++; if (arr[i] == 1) count1++; if (arr[i] == 2) count2++; }

// Putting the 0's in the array in starting.
for (int i = 0; i < count0; i++)
    arr[i] = 0;

// Putting the 1's in the array after the 0's.
for (int i = count0; i < (count0 + count1); i++)
    arr[i] = 1;

// Putting the 2's in the array after the 1's
for (int i = (count0 + count1); i < n; i++)
    arr[i] = 2;

return;

}

// Prints the array void printArray(int* arr, int n) { for (int i = 0; i < n; i++) printf("%d ", arr[i]); printf("\n"); }

// Driver code int main() { int arr[] = { 0, 1, 1, 0, 1, 2, 1, 2, 0, 0, 0, 1 }; int n = sizeof(arr) / sizeof(arr[0]); sort012(arr, n); printArray(arr, n); return 0; }

// This code is contributed by Aditya Kumar (adityakumar129)

Java

// Simple Java program to sort an array of 0s 1s and 2s. import java.lang.; import java.util.;

public class GfG {

public static void sort012(int arr[], int n)
{
    // Variables to maintain the count of 0's, 1's and
    // 2's in the array
    int count0 = 0, count1 = 0;
    int count2 = 0;
    for (int i = 0; i < n; i++) {
        if (arr[i] == 0)
            count0++;
        if (arr[i] == 1)
            count1++;
        if (arr[i] == 2)
            count2++;
    }

    // Putting the 0's in the array in starting.
    for (int i = 0; i < count0; i++)
        arr[i] = 0;

    // Putting the 1's in the array after the 0's.
    for (int i = count0; i < (count0 + count1); i++)
        arr[i] = 1;

    // Putting the 2's in the array after the 1's
    for (int i = (count0 + count1); i < n; i++)
        arr[i] = 2;

    printArray(arr, n);
}

// Prints the array
public static void printArray(int arr[], int n)
{
    for (int i = 0; i < n; i++)
        System.out.print(arr[i] + " ");
    System.out.println();
}

// Driver function
public static void main(String args[])
{

    int arr[] = { 0, 1, 1, 0, 1, 2, 1, 2, 0, 0, 0, 1 };
    int n = 12;
    sort012(arr, n);
}

}

// This code is contributed by Aditya Kumar (adityakumar129)

Python3

Python C++ program to sort an array of 0s

1s and 2s.

import math

def sort012(arr, n):

# Variables to maintain the count of 0's, 
# 1's and 2's in the array
count0 = 0
count1 = 0
count2 = 0
for i in range(0,n):
    if (arr[i] == 0):
        count0=count0+1
    if (arr[i] == 1):
        count1=count1+1
    if (arr[i] == 2):
        count2=count2+1


# Putting the 0's in the array in starting.
for i in range(0,count0):
    arr[i] = 0

# Putting the 1's in the array after the 0's.
for i in range( count0, (count0 + count1)) :
    arr[i] = 1

# Putting the 2's in the array after the 1's
for i in range((count0 + count1),n) :
    arr[i] = 2

return

Prints the array

def printArray( arr, n):

for i in range(0,n):
    print( arr[i] , end=" ")
print()

Driver code

arr = [ 0, 1, 1, 0, 1, 2, 1, 2, 0, 0, 0, 1 ] n = len(arr) sort012(arr, n) printArray(arr, n)

This code is contributed by Gitanjali.

C#

// Simple C# program // to sort an array of 0s // 1s and 2s. using System;

public class GfG{

public static void sort012(int []arr, int n)
{
    // Variables to maintain
    // the count of 0's, 
    // 1's and 2's in the array
    int count0 = 0, count1 = 0;
    int count2 = 0;
    for (int i = 0; i < n; i++) {
        if (arr[i] == 0)
            count0++;
        if (arr[i] == 1)
            count1++;
        if (arr[i] == 2)
            count2++;
    }

    // Putting the 0's in the
    // array in starting.
    for (int i = 0; i < count0; i++) 
        arr[i] = 0;

    // Putting the 1's in the
    // array after the 0's.
    for (int i = count0; i < 
        (count0 + count1); i++) 
        arr[i] = 1;

    // Putting the 2's in the
    // array after the 1's
    for (int i = (count0 + count1);
        i < n; i++) 
        arr[i] = 2;

    printArray(arr, n);
}

// Prints the array
public static void printArray(int []arr, int n)
{
    for (int i = 0; i < n; i++)
        Console.Write(arr[i] + " ");
    Console.WriteLine();
}

// Driver function 
public static void Main()
{

    int []arr = { 0, 1, 1, 0, 1, 2, 1,
                2, 0, 0, 0, 1 };
    int n = 12;
    sort012(arr, n);
}

}

// This code is contributed by vt_m

JavaScript

`

Output

0 0 0 0 0 1 1 1 1 1 2 2

**Time Complexity: O(n)
**Auxiliary Space: O(1)

**Problems with the above solution.:

1. It requires two traversals of array.
2. This solution may not work if values are a part of the structure. For example, consider a situation where 0 represents Computer Science Stream, 1 represents Electronics and 2 represents Mechanical. We have a list of student objects (or structures) and we want to sort them. We cannot use the above sort as we simply put 0s, 1s, and 2s one by one.

**Another Approach:

C++ `

// C++ program #include <bits/stdc++.h> using namespace std; // Example // // input = [0, 1, 2, 2, 0, 0] // output = [0, 0, 0, 1, 2, 2]

int main() {

vector<int> inputArray={0, 1, 1, 0, 1, 2, 1, 2, 0, 0, 0, 1};
vector<int> outputArray;
int indexOfOne = 0;
for(int item: inputArray)
{
    if(item==2)
    {   outputArray.push_back(item);
    }
    else if(item==1)
    {   outputArray.insert(outputArray.begin() + indexOfOne, item);
        indexOfOne+=1;
    }
    else if(item==0)
    {   outputArray.insert(outputArray.begin(), item);
        indexOfOne+=1;
    }
    else
    {   cout<<" wrong value - Aborting ";
        continue;
    }
}

for(int i=0;i<outputArray.size();i++)
{
    cout<<outputArray[i]<<" ";
}

return 0;

} // This code is contributed by Pushpesh Raj

Java

import java.util.ArrayList; import java.util.List;

// Example // // input = [0, 1, 2, 2, 0, 0] // output = [0, 0, 0, 1, 2, 2] class GFG { static int[] inputArray = { 0, 1, 1, 0, 1, 2, 1, 2, 0, 0, 0, 1 }; static List outputArray = new ArrayList<>(); static int indexOfOne = 0;

static void print() {
    for (int item : inputArray)
        if (item == 2)
            outputArray.add(item);
        else if (item == 1) {
            outputArray.add(indexOfOne, item);
            indexOfOne += 1;
        } else if (item == 0) {
            outputArray.add(0, item);
            indexOfOne += 1;
        } else {
            System.out.println(" wrong value - Aborting ");
            continue;
        }
}

public static void main(String[] args) {
    print();
    for (int item : outputArray)
        System.out.print(item+", ");
}

} // This code is contributed by Amit Katiyar

Python3

Example

input = [0, 1, 2, 2, 0, 0]

output = [0, 0, 0, 1, 2, 2]

inputArray = [0, 1, 1, 0, 1, 2, 1, 2, 0, 0, 0, 1] outputArray = [] indexOfOne = 0 for item in inputArray: if item == 2: outputArray.append(item) elif item == 1: outputArray.insert(indexOfOne, item) indexOfOne += 1 elif item == 0: outputArray.insert(0, item) indexOfOne += 1 else: print(" wrong value - Aborting ") continue print(outputArray)

C#

using System; using System.Collections.Generic;

// Example // // input = [0, 1, 2, 2, 0, 0] // output = [0, 0, 0, 1, 2, 2]

class GFG{

static int[] inputArray = { 0, 1, 1, 0, 1, 2, 1, 2, 0, 0, 0, 1 }; static List outputArray = new List(); static int indexOfOne = 0;

static void print() { foreach (int item in inputArray) if (item == 2) outputArray.Add(item); else if (item == 1) { outputArray.Insert(indexOfOne, item); indexOfOne += 1; } else if (item == 0) { outputArray.Insert(0, item); indexOfOne += 1; } else { Console.WriteLine(" wrong value - Aborting "); continue; } }

// Driver code public static void Main(String[] args) { print(); foreach(int item in outputArray) Console.Write(item + ", "); } }

// This code is contributed by 29AjayKumar

JavaScript

`

Output

0 0 0 0 0 1 1 1 1 1 2 2

**Time Complexity: O(n)
**Auxiliary Space: O(n)

**Optimal Solution that handles above issues : Sort an array of 0s, 1s and 2s (Dutch National Flag Algorithm)