int top = 0;
    int bottom = matrix.length - 1;
    int left = 0;
    int right = matrix[0].length - 1;

    while (top <= bottom && left <= right) {
        // move right
        for (int i = left; i <= right; i++) {
            result.add(matrix[top][i]);
        }
        top++;

        // move down
        for (int i = top; i <= bottom; i++) {
            result.add(matrix[i][right]);
        }
        right--;

        // move left
        if (top <= bottom) {
            for (int i = right; i >= left; i--) {
                result.add(matrix[bottom][i]);
            }
            bottom--;
        }

        // move up
        if (left <= right) {
            for (int i = bottom; i >= top; i--) {
                result.add(matrix[i][left]);
            }
            left++;
        }
    }

    return result;
}