Anti Diagonals - The Coding Shala

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Anti Diagonals Java Solution

Give an N*N square matrix, return an array of its anti-diagonals. Look at the example for more details.
Anti Diagonals Java Program - The Coding Shala
Example:

Input:  

1 2 3


7 8 9

4 5 6



Return the following :

[ 
  [1],
  [2, 4],  [3, 5, 7],
  [6, 8],
  [9]


]



Input : 

1 2
3 4



Return the following  : 

[
  [1],
  [2, 3],
  [4]


]

Anti Diagonals Java Solution

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public class Solution {
    public ArrayList<ArrayList<Integer>> diagonal(ArrayList<ArrayList<Integer>> A) {
        ArrayList<ArrayList<Integer>> ans = new ArrayList<ArrayList<Integer>>();
        int N = A.size();
        int i = N - 1;
        while(i>=0){
            ArrayList<Integer> tmp = new ArrayList<Integer>();
            int row = 0, col = N-i-1;
            for(int j=0;j<N-i;j++){
                tmp.add(A.get(row).get(col));
                row++;
                col--;
            }
            ans.add(tmp);
            i--;
        }
        i = N-2;
        while(i>=0){
            int row = N-i-1, col = N-1;
            ArrayList<Integer> tmp = new ArrayList<Integer>();
            for(int j=0;j<=i;j++){
                tmp.add(A.get(row).get(col));
                row++;
                col--;
            }
            ans.add(tmp);
            i--;
        }
        return ans;
    }
}



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Comments

  1. UnknownOctober 10, 2020 at 4:57 PM

    how can i solve this using array and not using collection framework classes

    ReplyDelete
    Replies
    1. Akshay KumarOctober 11, 2020 at 9:40 AM

      Change ArrayList to Array and all logic and process will be same, since return type is ArrayList so before returning you have to copy Array into ArrayList again that will be additional changes.

      Delete
  2. UnknownDecember 13, 2020 at 5:38 PM

    how can we change ArrayList to array having variable columns?

    ReplyDelete
    Replies
    1. UnknownDecember 13, 2020 at 5:56 PM

      public class Solution {
      public int[][] diagonal(int[][] a) {
      int n = a.length-1;
      ArrayList> otp = new ArrayList<>();

      for(int i=0; i temp = new ArrayList<>();
      int row = 0, col = i;
      while(col >= 0) {
      temp.add(a[row][col]);
      row++;
      col--;
      }
      otp.add(temp);
      }

      for(int i=1; i temp = new ArrayList<>();
      int row = i, col = n-1;
      while(row < n) {
      temp.add(a[row][col]);
      row++;
      col--;
      }
      otp.add(temp);
      }
      int[][] otpArray = new int[n+n-1][n+n-1];
      for(int i=0; i<otp.size(); i++)
      for(int j=0; j<otp.get(i).size(); j++)
      otpArray[i][j] = otp.get(i).get(j);

      return otpArray;
      }
      }

      Delete
    2. UnknownDecember 13, 2020 at 5:57 PM

      Its giving :
      [1 0 0 ] [2 4 0 ] [5 0 0 ]

      But it should:
      [1 ] [2 4 ] [3 5 7 ] [6 8 ] [9 ]

      Delete

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