MathDB
Maximum of a given substring in sequences

Source: 2021 SRMC P1

June 28, 2021

Problem Statement

Given a sequence ss consisting of digits 00 and 11. For any positive integer kk, define vkv_k the maximum number of ways in any sequence of length kk that several consecutive digits can be identified, forming the sequence ss. (For example, if s=0110s=0110, then v7=v8=2v_7=v_8=2, because in sequences 01101100110110 and 0110110001101100 one can find consecutive digits 01100110 in two places, and three pairs of 01100110 cannot meet in a sequence of length 77 or 88.) It is known that vn<vn+1<vn+2v_n<v_{n+1}<v_{n+2} for some positive integer nn. Prove that in the sequence ss, all the numbers are the same.
A. Golovanov