Leetcode Problem 54 Spiral Matrix.txt

54. Spiral Matrix
Given a matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order.

Example 1:

Input:
[
 [ 1, 2, 3 ],
 [ 4, 5, 6 ],
 [ 7, 8, 9 ]
]
Output: [1,2,3,6,9,8,7,4,5]
Example 2:

Input:
[
  [1, 2, 3, 4],
  [5, 6, 7, 8],
  [9,10,11,12]
]
Output: [1,2,3,4,8,12,11,10,9,5,6,7]


Hint to solve: Create 4 pointers. row_start, row_end, col_start, col_end.
Traverse in 4 directions. Update the pointers.

Edge case: inside the if condition check the size of the result.

public class Solution 
{
    
    public void DebugPrintList(IList<int> result)
    {
        foreach(var item in result)
        {
            Console.Write(item + " ");
        }
        Console.WriteLine();
    }
    
    public IList<int> SpiralOrder(int[][] matrix) 
    {
        IList<int> result = new List<int>();

        if(matrix == null || matrix.Count() == 0)
            return result;
        
        int row_start = 0;
        int col_start = 0;
        int row_end = matrix.Length;
        int col_end = matrix[0].Length;
        
        int totalElements = row_end*col_end;
        
        
        while(result.Count() != totalElements)
        {

            //Go from left to right. Record start row.
            for(int i = row_start; i<col_end && result.Count() != totalElements; ++i)
            {
                result.Add(matrix[row_start][i]);
            }
            row_start += 1;
            
            //Go from top to down. Record the last col.
            for(int i = row_start; i< row_end && result.Count() != totalElements; ++i)
            {
                result.Add(matrix[i][col_end-1]);
            }
            col_end -= 1;
            
            //Go from right to left. Record the last row.
            for(int i = col_end-1; i >= col_start && result.Count() != totalElements; --i)
            {
                result.Add(matrix[row_end-1][i]);
            }
            row_end -= 1;
            
            //Go from bottom to top. Record the start col.
            for(int i = row_end-1; i>= row_start && result.Count() != totalElements; --i)
            {
                result.Add(matrix[i][col_start]);
            }
            col_start += 1;
        }
        
        return result;
    }
}