Number of ways of placing balls subject to condition
Source:
December 31, 2011
combinatorics unsolvedcombinatorics
Problem Statement
Suppose there are boxes in a row and place balls in them one in each. The balls are colored red, blue or green. In how many ways can we place the balls subject to the condition that any box has at least one adjacent box having a ball of the same color as the ball in ? [Assume that balls in each color are available abundantly.]