Thinking process

http://www.programcreek.com/2013/01/leetcode-spiral-matrix-java/

if row and column are more than one, then there is a cycle

• two position variables, x and y

Mistakes

don't forget to break if the row or column is 1

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

        int rows = matrix.length;
        int cols = matrix[0].length;

        int x = 0;//current row position
        int y = 0;//current col position
        //[1,2,3]
        while (rows > 0 && cols > 0) {

            if (rows == 1) {
                for (int i = 0; i < cols; ++i) {
                    result.add(matrix[x][y++]);
                }
                break;
            }

            if (cols == 1) {
                for (int i = 0; i < rows; ++i) {
                    result.add(matrix[x++][y]);
                }
                break;
            }

            //top, left => right
            for (int i = 0; i < cols - 1; ++i) {
                result.add(matrix[x][y++]);
            }

            //right, top => bottom
            for (int i = 0; i < rows - 1; ++i) {
                result.add(matrix[x++][y]);
            }

            //bottom, right => left
            for (int i = 0; i < cols - 1; ++i) {
                result.add(matrix[x][y--]);
            }

            //left, bottom => top
            for (int i = 0; i < rows - 1; ++i) {
                result.add(matrix[x--][y]);
            }

            rows -= 2;
            cols -= 2;

            x++;
            y++;
        }


        return result;
    }
}

Follow up - 59. Spiral Matrix II

public class Solution {
    public int[][] generateMatrix(int n) {
        int[][] result = new int[n][n];

        int x = 0;
        int y = 0;
        int num = 1;

        while (n > 0) {
            if (n == 1) {
                result[x][y] = num;
                break;
            }

            //top, left => right
            for (int i = 0; i < n - 1; ++i) {
                result[x][y++] = num;
                num++;
            }

            //right, top => bottom 
            for (int i = 0; i < n - 1; ++i) {
                result[x++][y] = num;
                num++;
            }

            //bottom, right => left
            for (int i = 0; i < n - 1; ++i) {
                result[x][y--] = num;
                num++;
            }

            //left, bottom => top
            for (int i = 0; i < n - 1; ++i) {
                result[x--][y] = num;
                num++;
            }

            n -= 2;
            x++;
            y++;
        }

        return result;
    }
}