zoj1094 Matrix Chain Multiplication

1. //zoj1094   Matrix Chain Multiplication
2. //Accepted 1094 C++ 00:00.01 848K
3. #include <cstdio>
4. #include <iostream>
5. #include <string>
6. using namespace std;
7. struct matrix{ int row,col;}m[26],t[26];
8. int sum;
9. int index(char c){   return c-'A';}
10. void backtrack(string s)
11. {
12.        int i,j,k;
13.        if (s.length()==4){
14.               i = index(s[1]), j = index(s[2]);
15.               if (m[i].col==m[j].row){
16.                      sum += m[i].row*m[j].row*m[j].col;
17.                      cout << sum << endl;
18.               }else cout << "error" << endl;
19.               return;
20.        }
21.        for (k=1; s[k]!=')'; ++k);
22.        i = index(s[k-2]), j = index(s[k-1]);
23.        if (m[i].col==m[j].row){
24.               sum += m[i].row*m[j].row*m[j].col;
25.               m[i].col = m[j].col;
26.               s.erase(k-1,2);
27.               s.erase(k-3,1);
28.               backtrack(s);
29.        }else cout << "error" << endl;
30. }
31. int main()
32. {
33. #ifdef ONLINE_JUDGE
34. #else
35.        freopen("1094.txt","r",stdin);
36. #endif
37.        int i,n;
38.        cin>>n;
39.        char c;
40.        for (i=0; i<n; ++i)
41.               cin >> c >> t[i].row >> t[i].col;
42.        string s;
43.        while (cin >> s){
44.               if (s.length()==1){
45.                      cout << 0 << endl;
46.                      continue;
47.               }
48.               for (i=0; i<n; ++i) m[i].row = t[i].row, m[i].col = t[i].col;
49.               sum = 0;
50.               backtrack(s);
51.        }
52. #ifdef ONLINE_JUDGE
53. #else
54.        fclose(stdin);
55. #endif
56.        return 0;
57. }