UVA442-Matrix Chain Multiplication

紫书代码：
 1 #include<cstdio>
 2 #include<string>
 3 #include<algorithm>
 4 #include<iostream>
 5 #include<stack>
 6 using namespace std;
 7 
 8 struct Matrix
 9 {
10     int a,b;
11     Matrix(int a=0,int b=0):a(a),b(b) {}
12 }m[26];
13 
14 stack<Matrix> s;
15 
16 int main()
17 {
18     int n;
19     cin>>n;
20     for(int i=0;i<n;i++)
21     {
22         string name;
23         cin>>name;
24         int k=name[0]-'A';
25         cin>>m[k].a>>m[k].b;
26     }
27     string expr;
28     while(cin>>expr)
29     {
30         int len=expr.length();
31         bool error=false;
32         int ans=0;
33         for(int i=0;i<len;i++)
34         {
35             if(isalpha(expr[i]))s.push(m[expr[i]-'A']);
36             else if(expr[i]==')')
37             {
38                 Matrix m2=s.top();s.pop();
39                 Matrix m1=s.top();s.pop();
40                 if(m1.b!=m2.a){error=true;break;}
41                 ans+=m1.a*m1.b*m2.b;
42                 s.push(Matrix(m1.a,m2.b));
43             }
44         }
45         if(error)printf("error
");
46         else printf("%d
",ans);
47     }
48     return 0;
49 }