Spiral Matrix

Spiral Matrix array

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]

Spiral Matrix Solution

class SpiralMatrix {
    public List<Integer> spiralOrder(int[][] matrix) {
        List<Integer> result = new ArrayList<Integer>();
        if(matrix == null || matrix.length == 0) {
            return result;
        }

        int rowStart = 0;
        int rowEnd = matrix.length - 1;
        int colStart = 0;
        int colEnd = matrix[0].length - 1;
        while(rowStart <= rowEnd && colStart <= colEnd) {
            for(int i = colStart; i <= colEnd; i++) {
                result.add(matrix[rowStart][i]);
            }
            rowStart++;

            for(int i = rowStart; i <= rowEnd; i++) {
                result.add(matrix[i][colEnd]);
            }
            colEnd--;

            if(rowStart <= rowEnd) {
                for(int i = colEnd; i >= colStart; i--) {
                    result.add(matrix[rowEnd][i]);
                }
            }
            rowEnd--;

            if(colStart <= colEnd) {
                for(int i = rowEnd; i >= rowStart; i--) {
                    result.add(matrix[i][colStart]);
                }
            }
            colStart++;
        }

        return result;
    }
}

Last modified October 4, 2020