
ZOJ Problem Set  1094
Matrix multiplication problem is a typical example of dynamical programming. Suppose you have to evaluate an expression like A*B*C*D*E where A,B,C,D and E are
matrices.
Since matrix multiplication is associative, the order in which multiplications are
performed is arbitrary. However, the number of elementary multiplications needed
strongly depends on the evaluation order you choose. Your job is to write a program that determines the number of elementary multiplications needed for a given evaluation strategy. Input SpecificationInput consists of two parts: a list of matrices and a list of expressions.The first line of the input file contains one integer n (1 <= n <= 26), representing the number of matrices in the first part. The next n lines each contain one capital letter, specifying the name of the matrix, and two integers, specifying the number of rows and columns of the matrix. The second part of the input file strictly adheres to the following syntax (given in EBNF):
SecondPart = Line { Line } <EOF> Line = Expression <CR> Expression = Matrix  "(" Expression Expression ")" Matrix = "A"  "B"  "C"  ...  "X"  "Y"  "Z"
Output SpecificationFor each expression found in the second part of the input file, print one line containing the word "error" if evaluation of the expression leads to an error due to nonmatching matrices. Otherwise print one line containing the number of elementary multiplications needed to evaluate the expression in the way specified by the parentheses.Sample Input9 A 50 10 B 10 20 C 20 5 D 30 35 E 35 15 F 15 5 G 5 10 H 10 20 I 20 25 A B C (AA) (AB) (AC) (A(BC)) ((AB)C) (((((DE)F)G)H)I) (D(E(F(G(HI))))) ((D(EF))((GH)I)) Sample Output0 0 0 error 10000 error 3500 15000 40500 47500 15125 Source: University of Ulm Local Contest 1996 