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CIIM 2009 Problem 3

Source:

June 9, 2016
CIIM 2009CIIMundergraduate

Problem Statement

Let r>nr > n be positive integers. A "good word" is an nn-tuple a1,,an\langle a_1,\dots, a_n \rangle of distinct positive integers between 1 and rr. A "play" consist of changing a integer aia_i of a good word, in such a way that the resulting word is still a good word. The distance between two good words A=a1,,anA= \langle a_1,\dots, a_n \rangle and B=b1,,bnB = \langle b_1,\dots, b_n \rangle is the minimun number of plays needed to obtain B from A. Find the maximun posible distance between two good words.