Balanced bracket sequences

2021 VietMX 0

1. Overview A balanced bracket sequence is a string consisting of only brackets, such that this sequence, when inserted certain numbers and mathematical operations, gives a valid […]

Dima and Two Sequences

2020 VietMX 0

Little Dima has two sequences of points with integer coordinates: sequence (a 1, 1), (a 2, 2), …, (a n, n) and sequence (b 1, 1), (b 2, 2), …, (b n, n). Now Dima wants to count the number of distinct sequences of points of […]