Source: Tanya Khovanova’s Math Blog
Problem: The Sultan decided to test the wisdom of his wizards. He collected them together and gave them a task. Tomorrow at noon he will put hats of different colors on each of the wizard’s heads.
The wizards have a list of the available colors. There are enough hats of each color for every wizard. The wizards also have a list of rooms. There are enough rooms to assign a different room for every color.
Tomorrow as the Sultan puts hats on the wizards, they will be able to see the colors of the hats of the other wizards, but not the color of their own. Without communicating with each other, each wizard has to choose a room. The challenge comes when two wizards have the same hat color, for they must choose the same room. On the other hand, if they have different hat colors, they must choose different rooms. Wizards have one day to decide on their strategy. If they do not all complete their task, then all of their heads will be chopped off. What strategy would you suggest for the wizards?
Update (Dec 04, 2010)
Solution: One solution posted by Siddhant Agarwal (EE 4th year, IITB) in comments! Another solution posted independently by Hasan Kumar Reddy (mintuhouse) (CSE 2nd year, IITB) and Saurabh Joshi (PhD Student, CSE, IITK). Thanks.