矩阵链乘（UVa 442)

　　结构体 struct matrix 用来保存矩阵的行和列；

　　map<string,matrix> 用来保存矩阵名和相应的行列数；

　　stack<string> 用来保存表达式中遇到的矩阵名，并将每次乘法运算后的矩阵压入栈中；

C++11 代码如下：

 #include<iostream>
 #include<map>
 #include<string>
 #include<stack>
 using namespace std;

 struct matrix {
     int row;
     int column;
 };

 int main() {
     int n; string ch;
     string str;
     int li, co;
     map<string, matrix>m;
     cin >> n;
     for (int i = ; i < n; i++) {
         cin >> ch >> li >> co;
         m[ch].row = li;
         m[ch].column = co;
     }
     while ((cin >> str)){
         stack<string>s;
         string a, b;
         int sum = ;
         bool flag = true;
         for (int i = ; i < str.length(); i++) {
             if (str[i] == '(') continue;
             else if (str[i] == ')') {
                 a = s.top(); s.pop();
                 b = s.top(); s.pop();
                 if (m[b].column == m[a].row) {
                     sum += m[b].row*m[b].column*m[a].column;
                     string ba;
                     ba = b + a;
                     s.push(ba);
                     m[ba].row = m[b].row;
                     m[ba].column = m[a].column;
                 }
                 else {
                     flag = false;
                     break;
                 }
             }
             else {
                 string s2;
                 s2 = str[i];
                 s.push(s2);
             }
         }
         if(flag) cout << sum << endl;
         else cout << "error" << endl;
     }
     return ;
 }