Riff A - Intro
G|---------------------------------------------------------|
D|---------------------------------------------------------|
A|---------------------------------------------------------|
E|--2-3-3-3--3-3--2-3-3-3--3-3--2-3-3--2-3-3--2-3-3--2-3-3-|

  Riff B
G|--------------------------|
D|--------------------------| x 3
A|------------------3--2--3-|
E|--3-3-3-3-3-3-3-3---------|

G|----------------------------------|
D|----------------------------------|
A|----------------------------------|
E|--3-3-3-3-3-3-3-3-3-3-3-3-3-3-3-3-|

  Alternate Riff B
G|--------------------------|
D|--------------------------| x 2
A|------------------3--2--3-|
E|--3-3-3-3-3-3-3-3---------|

G|--------------------------------------------------------------------|
D|--------------------------------------------------------------------|
A|------------------5-5-5-5-5-5-5-5-----------------------------------|
E|--3-3-3-3-3-3-3-3-----------------3-3-3-3-3-3-3-3-3-3-3-3-3-3-3-3-3-|

  Riff C
G|---------------------------------|
D|---------------------------------| x 4
A|--5-5-5------4-5-5-5-5-5-5-5-5-5-|
E|--------5--5---------------------|

  Riff D - Guitar solo
G|----------------------------------------------------------------------------------------|
D|----------------------------------------------------------------------------------------|
A|--2-2-2-2-2-2-2-2-0-0-0-0-0-0-0-0-2-2-2-2-2-2-2-2-0-0-0-0-0-0-0-0-2-2-2-2-2-2-2-2-0-0-0-|
E|----------------------------------------------------------------------------------------|

G|-----------------------------------------------------------|
D|-----------------------------------------------------------|
A|-0-0-0-0-0-2-2-2-2-2-2-2-2-4-5-5-5-4-5-5-5-4-5-5-5-4-5-5-5-|
E|-----------------------------------------------------------|

  Riff E - Outro
G|---------------------------------      ----------------------------------|
D|--------------------------------- x 3  ----------------------------------|
A|--3--3-3-3-3-3-3-2-2-2-2-0-0-0-0-      ----------------------------------|
E|---------------------------------      --2-3-3-3-3-3-3-3-2-3-3-3-3-3-3-3-|

G|-------------------------------------------------|
D|-------------------------------------------------|
A|-------------------------------------------------|
E|--2-3-3-3--3-3--2-3-3-3--3-3--2-3-3--2-3-3--3----|

to know when you have to switch between Riff B and Alternate Riff B just listen to the 
other than that its pretty simple