class Solution {
    public List<Integer> spiralOrder(int[][] matrix) {
        int up=0, down=matrix.length-1, left=0, right=matrix[0].length-1;
        List<Integer> list = new ArrayList<>();
        while(up<=down && left<=right){
            for(int i=left; i<=right; i++)
                list.add(matrix[up][i]);
            up++;
            if(up>down || left>right) break;
            for(int i=up; i<=down; i++)
                list.add(matrix[i][right]);
            right--;
            for(int i=right; i>=left; i--)
                list.add(matrix[down][i]);
            down--;
            if(up>down || left>right) break;
            for(int i=down; i>=up; i--)
                list.add(matrix[i][left]);
            left++;
        }
        return list;
    }
}