Java Program to Sort 2D Array Across Columns - GeeksforGeeks

18 Mar, 2022
The Vector class implements a growable array of objects. Vectors basically fall in legacy classes but now it is fully compatible with collections. It is found in the java.util package and implements the List interface, so we can use all the methods of List interface here. This program is used to Sort the 2D array Across Columns. We will use the concept of vector to sort each column.
Algorithm:
Traverse each column one by one.Add elements of Column 1 in vector v.Sort the vector.Push back the sorted elements from vector to column.Empty the vector by removing all elements for fresh sorting.Repeat the above steps until all columns are done.
Traverse each column one by one.
Add elements of Column 1 in vector v.
Sort the vector.
Push back the sorted elements from vector to column.
Empty the vector by removing all elements for fresh sorting.
Repeat the above steps until all columns are done.
Illustration: Creating a Vector 
Here we are creating a default vector of the initial capacity is 10 so do the syntax is as follows:
Vector<E> v = new Vector<E>();
Functions that will be used in order to achieve the goal are as follows: 
A. removeAll(): The java.util.vector.removeAll(Collection col) method is used to remove all the elements from the vector, present in the collection specified.
Syntax:
Vector.removeAll(Vector)  
B. Collections.sort(): This method is used to sort the vector.
Syntax:
Collections.sort(Vector)
C. add(): This method is used to add elements in the vector.
Syntax:
Vector.add(value)
D. get(): This method will get the element of Vector stored at a particular index
Syntax:
Vector.get(3);
Example
Java
// Java Program to Sort 2D array across Columns // Importing required classesimport java.io.*;import java.lang.*;import java.util.*; // Main classclass GFG {     // Main driver method    public static void main(String[] args)        throws java.lang.Exception    {         // Custom input for 2D array        int[][] arr = { { 7, 2, 0, 5, 1 },                        { 3, 8, 2, 9, 14 },                        { 5, 1, 0, 5, 2 },                        { 4, 2, 6, 0, 1 } };         // Display message for better readability        System.out.println("Matrix without sorting \n");         // Nested iteration to display matrix        for (int i = 0; i < 4; i++) {             for (int j = 0; j < 5; j++) {                 // Printing elements of 2D matrix                System.out.print(arr[i][j] + " ");            }            // New line as we are done with row            System.out.println();        }         // Creating an object of Vector class        Vector<Integer> v = new Vector<>();         // Nested iteration using for loops        for (int i = 0; i < 5; i++) {            for (int j = 0; j < 4; j++) {                 // Adding elements of columns in vector                // using add() method                v.add(arr[j][i]);            }             // Sorting elements in vector            // using sort() method            Collections.sort(v);             for (int j = 0; j < 4; j++) {                 // Sorted elements are pushed back                // from vector to column                arr[j][i] = v.get(j);            }             // Elements are removed from vector for            // fresh sorting using remove() method            v.removeAll(v);        }         // Printing matrix after sorting        System.out.println("Matrix after sorting \n");         for (int i = 0; i < 4; i++) {            for (int j = 0; j < 5; j++) {                 System.out.print(arr[i][j] + " ");            }             System.out.println();        }    }}
Matrix without sorting 

7 2 0 5 1 
3 8 2 9 14 
5 1 0 5 2 
4 2 6 0 1 
Matrix after sorting 

3 1 0 0 1 
4 2 0 5 1 
5 2 2 5 2 
7 8 6 9 14 
 Auxiliary Space : O(1)
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