spiral message - code practice - September 3, 2017

spiralMessage_practice2.cs

using System;

class Solution
{
    public static int[] SpiralCopy(int[,] inputMatrix)
    {
      // your code goes here
      if(inputMatrix == null || inputMatrix.GetLength(0) == 0 || inputMatrix.GetLength(1) == 0)
      {
        return new int[0]; 
      }
      
      var rows    = inputMatrix.GetLength(0); 
      var columns = inputMatrix.GetLength(1); 
      
      var startRow = 0;  //0
      var startCol = 0;  // 0
      var endRow = rows - 1; // 3
      var endCol = columns - 1; // 0
      
      // 5
      // 10
      // 15
      // 20
        
      var spiral = new int[rows * columns]; // 4
      var index = 0; 
      
      while(startRow <= endRow && startCol <= endCol ) // 0 <= 3, 0 <= 0
      {
        // four loops
        // top row 
        for(var col = startCol; col <= endCol; col++)  // 5
        {
          var visit = inputMatrix[startRow, col]; 
          spiral[index] = visit; 
          index++; 
        }
        
        // last column
        for(var row = startRow + 1 ; row <= endRow; row++) // from 1 to 3 in row, 10, 15, 20
        {
          var visit = inputMatrix[row, endCol]; 
          spiral[index] = visit; 
          index++; 
        }
        
        // last row, check edge case: one row
        for(var col = endCol - 1; col >= startCol && endRow > startRow; col --)  // add one more condition
        {
          var visit = inputMatrix[endRow, col]; 
          spiral[index] = visit; 
          index++; 
        }
        
        // first column 
        for(var row = endRow - 1; row > startRow && endCol > startCol; row --)  // add one more condition
        {
          var visit = inputMatrix[row, startCol]; 
          spiral[index] = visit; 
          index++; 
        }
        
        startRow ++; 
        endRow --; 
        startCol ++; 
        endCol --; 
      }
      
      return spiral; 
    }

    static void Main(string[] args)
    {
       var inputMatrix = new int[,]{{1}}; 
       var result = SpiralCopy( inputMatrix); 
       Console.WriteLine(result[0]); 
    }
}

// 0, 0 
// first row, 1 - 5, 
// last column, second row to last row , 20 is in second iteration, 
// last row, next to last column, 19 - 16
// first column, next to last row -> 6, 6 is next to first row
// start pointer 1, 1, start again 4 loops from 7
// edge case: if it is one row, we do not visit twice, one row, no two rows, left -> right
// edge case: if it is one column, we start from top to down
// one element -> 
// while loop