Question

Implement a method/function in java that produces running sum

runningSum2DArray(int[][] array, int dir) across rows (left to right or right to left) or columns (top to bottom or bottom to top)

Input to the method: A 4x4 two dimensional int array and an integer (1, 2, 3 or 4 for left, right, up,down respectively).

Output: The modified array after producing the running sums according to the direction.

For example: If the input to the method is the same as the earlier array, and if the direction is 2 (right), the output array would be printed as:

10 25 55 95

15 20 28 30

20 22 26 28

1 5 10 10

Now, implement another function runningSum2DArrayList(ArrayList< ArrayList< Integer > > list, int dir) that performs the same functionality.

Answer 1

For the above things, we need to have the following things into consideration.

1. We need to go according to the direction.
   1. One(1) indicates, going to left from right
   2. Two(2) indicates, going to the right from left
   3. Three(3) indicates, going to top from the bottom
   4. Four(4) indicates, going to bottom from top

Following is the code for the same.

import java.util.ArrayList;

public class FindingTheSums {
   public static void Sum2DArray(int arr[][], int dir) {
       if(dir == 1)
       {
           // Left
           for(int i=0;i<arr.length;i++) {
               for(int j = arr[0].length-2;j>=0;j--) {
                   arr[i][j] = arr[i][j+1] + arr[i][j];
               }
           }
       }
       else if(dir == 2)
       {
           // right
           for(int i = 0;i<arr.length;i++) {
               for(int j = 1;j<arr[0].length;j++) {
                   arr[i][j] = arr[i][j-1] + arr[i][j];
               }
           }
       }
       else if(dir == 3)
       {
           // top
           for(int j = 0;j<arr[0].length;j++) {
               for(int i = arr.length-2;i>=0;i--) {
                   arr[i][j] = arr[i][j] + arr[i+1][j];
               }
           }
       }
       else
       {
           // down
           for(int j = 0;j<arr[0].length;j++) {
               for(int i = 1;i<arr.length;i++) {
                   arr[i][j] = arr[i][j] + arr[i-1][j];
               }
           }
       }
   }
   public static void print(int arr[][]) {
       for(int i = 0 ;i<arr.length;i++) {
           for(int j = 0;j<arr[0].length;j++) {
               System.out.print(arr[i][j] + " ");
           }
           System.out.println();
       }
       System.out.println();
   }
   public static void main(String args[]) {
       int arr[][] = {{10, 15, 30, 40},{15, 5, 8, 2},{20, 2, 4, 2},{1, 4, 5, 0}};
       Sum2DArray(arr, 2);
       print(arr);
   }

}

Following is the output snippet of the above program.

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