Words with a, b and c (2)

In this problem we consider words of size n made up only of letters ‘a’,
‘b’ and ‘c’, and without two or more consecutive equal letters. Suppose
that some positions of the word have fixed letters. Write a program to
count all the words that meet these constraints.

Input

Input consists of several cases. Every case starts with n, followed by
the number of fixed positions f, followed by f pairs p_(i) c_(i), where
p_(i) is a position between 0 and n − 1 and c_(i) is ‘a’, ‘b’ or ‘c’.
Suppose 1 ≤ n ≤ 10⁴, 0 ≤ f ≤ n, and that all p_(i)’s are different.

Output

For every case, print the number of words that satisfy the constraints
modulo 10⁸ + 7.

Problem information

Author: Unknown
Translator: Salvador Roura

Generation: 2026-01-25T11:32:58.365Z

© Jutge.org, 2006–2026.
https://jutge.org
