54. Spiral Matrix

54. Spiral Matrix

Medium

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]

Solution:

    /* startR - starting row index 

       endR - ending row index 

        startC - starting column index 

        endC - ending column index 

class Solution {
    public List<Integer> spiralOrder(int[][] matrix) {
        List<Integer> res = new ArrayList<Integer>();
        if(matrix == null) return null;
        if(matrix.length == 0 || matrix[0].length == 0) return res;
        int startR = 0;
        int startC= 0;
        int endR = matrix.length -1;
        int endC = matrix[0].length-1;

         //test case {{1},{2},{3},{4}}
        while(startR <= endR && startC <= endC){//both satisfied
            spiralOneLayer(matrix,res,startR,endR,startC,endC);
        startR++;
        endR--;
        startC++;
        endC--;
        }
        return res;
        
    }
    
    private void spiralOneLayer(int[][] matrix, List<Integer> res, int startR, int endR, int startC, int endC){
        System.out.print(startC+"-"+ endC);
        if(startR == endR){// when there is one row
            for(int i = startC; i <= endC; i++){
                res.add(matrix[startR][i]);  
            }
        }else if(startC == endC){// when there is one column
            for(int i = startR; i <= endR; i++){
                res.add(matrix[i][startC]);  
            }
        }else{        
        if(startC < endC){
            for(int i = startC; i < endC; i++){
                res.add(matrix[startR][i]);   
            } 
        }
        if(startR < endR){
            for(int i = startR; i < endR; i++){
                res.add(matrix[i][endC]);  
            }
        }
        if(startR < endR){
            for(int i = endC; i > startC; i--){
                res.add(matrix[endR][i]); 
            }
        }
        if(startC < endC){
            for(int i = endR; i > startR; i--){
                res.add(matrix[i][startC]);  
            }
        }
       }
    }
}