UVa 442 (栈) Matrix Chain Multiplication

 1 #include <cstdio>
 2 #include <cstring>
 3 
 4 const int maxn = 30;
 5 int n;
 6 char s[100];
 7 
 8 struct Matrix
 9 {
10     int n, m;
11     Matrix(int n=0, int m=0):n(n), m(m) {}
12     int times(const Matrix& rhs) const
13     {
14         if(m == rhs.n) return n * m * rhs.m;
15         return -1;
16     }
17     Matrix operator * (const Matrix& rhs) const
18     { return Matrix(n, rhs.m); }
19 }mat[maxn], stack[maxn];
20 
21 int ID(char c) { return c - ‘A‘; }
22 
23 int main()
24 {
25     //freopen("in", "r", stdin);
26     scanf("%d", &n);
27     getchar();
28     for(int i = 0; i < n; ++i)
29     {
30         int n, m;
31         char name;
32         scanf("%c %d %d", &name, &n, &m);
33         getchar();
34         mat[ID(name)] = Matrix(n, m);
35     }
36 
37     while(scanf("%s", s) == 1)
38     {
39         int l = strlen(s);
40         int ans = 0, p = 0, ok = 1;
41         for(int i = 0; i < l; ++i)
42         {
43             if(s[i] == ‘(‘) continue;
44             else if(s[i] == ‘)‘)
45             {
46                 Matrix B = stack[--p];
47                 Matrix A = stack[--p];
48                 int t = A.times(B);
49                 if(t != -1)
50                 {
51                     ans += t;
52                     stack[p++] = A * B;
53                 }
54                 else { ok = 0; break; }
55             }
56             else
57             {
58                 stack[p++] = mat[ID(s[i])];
59             }
60         }
61 
62         if(ok) printf("%d\n", ans);
63         else puts("error");
64     }
65 
66     return 0;
67 }