Spiral Matrix

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

For example, Given the following matrix:

[ [ 1, 2, 3 ],

[ 4, 5, 6 ],

[ 7, 8, 9 ] ]

You should return [1,2,3,6,9,8,7,4,5].

Java代码：

public ArrayList<Integer> spiralOrder(int[][] matrix) {
        ArrayList<Integer> result = new ArrayList<Integer>();

        if(matrix == null || matrix.length == 0) return result;

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

        int x=0;
        int y=0;

        while(rows>0 && cols>0){

            //if one row/column left, no circle can be formed
            if(rows==1){
                for(int i=0; i<cols; i++){
                    result.add(matrix[x][y++]);
                }
                break;
            }else if(cols==1){
                for(int i=0; i<rows; i++){
                    result.add(matrix[x++][y]);
                }
                break;
            }

            //below, process a circle

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

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

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

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

            x++;
            y++;
            rows=rows-2;
            cols=cols-2;
    }

    return result;
}