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Sort an arrays of 0’s, 1’s and 2’s using Java
Given an array of 0, 1 and 2 sort the element in an order such that all the zeros come first before 1 and all the 2’s in the end. We have to sort all the elements of the array in-place.
We can solve this problem using DNF (Dutch National Flag) Sorting Algorithm. For example,
Input-1 −
arr[ ]= {2,0,0,1,2,1 }Output −
0 0 1 1 2 2
Explanation − Sorting the given array of elements containing 0,1 and 2 using the DNF Sorting Algorithm, it will print the output as {0,0,1,1,2,2}.
Input-2 −
arr[ ] = {0,1,1,2,1,1,0}Output −
0 0 1 1 1 1 2
Explanation − Sorting the given array of elements containing 0,1 and 2 using the DNF Sorting Algorithm, it will print the output as {0,0,1,1,1,1,2}.
Approach to solve this problem
In the given array of 0, 1, and 2 we can use the DNF sorting algorithm.
DNF Sorting Algorithm − The algorithm requires 3 pointers to iterate throughout the array by swapping the necessary elements.
Create a low pointer at the beginning of the array and a high pointer pointing at the end of the array.
Find the Midpoint of the array and create a mid-pointer as well that iterates from the beginning of the array till the end.
If the mid pointer of the array is ‘0’, then swap the element pointing at low. Increment the low pointer and mid pointer.
If the mid-pointer of the array is ‘2’, then swap it with the element pointing at the high. Increment the mid pointer and decrement the high pointer.
If the mid-pointer of the array is ‘1’, then increase the mid pointer.
Example
public class Solution {
public static void binarySorting(int arr[], int n){
int low=0;
int high= n-1;
int mid=0;
while(mid<=high){
if(arr[mid]==0){
int temp= arr[mid];
arr[mid]= arr[low];
arr[low]= temp;
mid++;
low++;
}
if(arr[mid]==1){
mid++;
}
if(arr[mid]==2){
int temp= arr[mid];
arr[mid]= arr[high];
arr[high]= temp;
high--;
}
}
}
public static void print(int arr[], int n){
for (int i = 0; i < n; i++)
System.out.print(arr[i] +" ");
}
public static void main(String[] args){
int arr[] ={ 0,0,1,0,1,0,1,2,2};
int n = arr.length;
binarySorting(arr, n);
print(arr, n);
}
}Output
Running the above code will generate the output as,
0 0 0 0 1 1 1 1 2
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