zoj 1094 Matrix Chain Multiplication 栈应用

//利用stack计算表达式
//类似计算中序表达式那样，用两个栈，一个存字母，一个存符号
//这题要自己存入*号，要用一个变量储存之前输入的符号，判断是否要把*入栈
//如果前一个符号是（，则不需要。
#include <iostream>
#include <stack>
#include <cstdio>
using namespace std; 

struct info
{
    int row, col;
    info() {}
    info (int row, int col)
    {
        this->row = row;
        this->col = col;
    }
}; 

const int N = 30;
stack<char> oprator;
stack<info> matrix; 

info a[N];
int n; 

int main()
{
    char c, s, last;
    int ans = 0;
    info num1, num2;
    bool isError;
    while (cin >> n)
    {
        for (int i = 0; i < n; i++)
            cin >> c >> a[i].row >> a[i].col; 

        isError = false;
        getchar();
        last = '(';
        while (scanf("%c", &c) != EOF)
        {
            if (c == '\n')
            {
                if (isError)
                    cout << "error" << endl;        
                else        
                    cout << ans << endl;
                while (!matrix.empty())
                    matrix.pop();
                while (!oprator.empty())
                    oprator.pop();
                isError = false;
                ans = 0;
                last = '(';
                continue;
            }
            if (isError)
                continue;
            if (c == '(')
            {
                if (last != c)
                    oprator.push('*');
                oprator.push(c);
                last = c;
            }
            else if (c == ')')
            {
                s = oprator.top();
                oprator.pop();
                while (s != '(')
                {
                    num1 = matrix.top();
                    matrix.pop();
                    num2 = matrix.top();
                    matrix.pop();
                    if (num2.col != num1.row)
                        isError = true;
                    else
                    {
                        ans += num2.row*num2.col*num1.col;
                        matrix.push(info(num2.row, num1.col));
                    }
                    s = oprator.top();
                    oprator.pop();
                }
                last = '0';
            }
            else
            {
                if (last != '(')
                    oprator.push('*');
                matrix.push(info(a[c-'A'].row, a[c-'A'].col));
                last = c;
            }
        }
    }
    return 0;
}