Sorts Array containing only 0s, 1s, 2s

java/sagar2002malik_sort012.java

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+// Problem Statement -
+// Given an array containing only 0's, 1's, and 2's. Sort the given array in increasing order and in linear time.
+
+// Solution
+import java.io.*;
+import java.util.*;
+
+public class main {
+
+  public static void sort012(int[] arr){
+    //write your code here
+
+    // Take 3 variables for defining regions for 0 , 1 and 2.
+    int j=0; // 0 to j-1 -> 0's area
+    int i=0; // j to i-1 -> 1's area
+    int k=arr.length-1; // k+1 to end -> 2's area
+
+    // Initially unknown area is i to k
+
+    //  loop will run till there are unknowns left
+    while(i<=k){
+        if(arr[i]==1){
+            i++;
+        }
+        else if(arr[i]==0){
+            swap(arr,i,j);
+            i++;j++;
+        }
+        else{
+            swap(arr,i,k);
+            k--;
+        }
+    }
+
+  }
+
+  // used for swapping ith and jth elements of array
+  public static void swap(int[] arr, int i, int j) {
+    System.out.println("Swapping index " + i + " and index " + j);
+    int temp = arr[i];
+    arr[i] = arr[j];
+    arr[j] = temp;
+  }
+
+  public static void print(int[] arr){
+    for(int i = 0 ; i < arr.length; i++){
+      System.out.println(arr[i]);
+    }
+  }
+  public static void main(String[] args) throws Exception {
+    Scanner scn = new Scanner(System.in);
+    System.out.println("Enter the length of array");
+    int n = scn.nextInt();
+    int[] arr = new int[n];
+    System.out.println("Enter the elements of the array");
+    for(int i = 0 ;i < n; i++){  
+      arr[i] = scn.nextInt();
+    }
+    sort012(arr);
+    print(arr);
+  }
+
+}