class Solution {
    public List<Integer> spiralOrder(int[][] matrix) {
        List<Integer> res = new ArrayList();

        if(matrix.length==0) return res;

        int rowBegin = 0;
        int rowEnd = matrix.length-1;
        int columnBegin = 0;
        int columnEnd = matrix[0].length-1;

        while(rowBegin <= rowEnd && columnBegin <= columnEnd){
            for(int i =columnBegin; i<= columnEnd; i++){
                res.add(matrix[rowBegin][i]);
            }
            rowBegin++;

            for(int i =rowBegin; i<=rowEnd; i++){
                res.add(matrix[i][columnEnd]);
            }
            columnEnd--;

            if(rowBegin <= rowEnd){
                for(int i= columnEnd; i>=columnBegin; i--){
                    res.add(matrix[rowEnd][i]);
                }
                rowEnd--;
            }

            if(columnBegin<=columnEnd){
                for(int i=rowEnd; i>=rowBegin; i--){
                    res.add(matrix[i][columnBegin]);
                }
                columnBegin++;
            }
        }
        return res;
    }
}