ZOJ1094 POJ2246 Matrix Chain Multiplication

第一次在这里贴算法题，如有不足希望大家指教。

/*
 * =====================================================================================
 *
 *       Filename:  ZOJ1094_POJ2246_Matrix_Chain_Multiplication.cpp
 *
 *    Description:  
 *
 *        Version:  1.0
 *        Created:  2013/5/11 13:37:06
 *       Revision:  none
 *       Compiler:  gcc
 *
 *         Author:  Neo Fung (http://www.neofung.org), iam AT neofung DOT org
 *   Organization:  
 *
 * =====================================================================================
 */
#include <stdlib.h>
#include <stdio.h>
#include <iostream>
#include <string>
#include <vector>
#include <stack>
#include <map>
#include <math.h>
#include <algorithm>
#include <numeric>
#include <functional>

using namespace std;

int main(void)
{
    //ifstream cin("data.txt");
    pair<int,int> A,B,TEMP,alap2pair[26];
    char alaph[128]={0};
    char ch;
    int a,b;
    string str;
    stack<pair<int,int> > mystack;
    int n;
    cin>>n;
    int i,j,k;
    for(i=0;i<n;++i)
    {
        cin>>ch>>a>>b;
        alaph[ch]=i;
        alap2pair[i]=make_pair(a,b);
    }

    while(cin>>str)
    {
        int length(str.length());
        int sum(0);
        while(!mystack.empty()) mystack.pop();
        for(i=0;i<length;++i)
        {
            if(str.at(i) ==')')
            {                
                B = mystack.top();
                mystack.pop();
                A = mystack.top();
                mystack.pop();
                if (A.second != B.first)
                {
                    sum =-1;
                    break;
                }
                sum += A.first * A.second * B.second;
                TEMP = make_pair(A.first,B.second);
                mystack.pop();
                mystack.push(TEMP);
            }
            else
            {
                if (str.at(i) == '(')
                {
                    mystack.push(make_pair(0,0));
                }
                else
                    mystack.push(alap2pair[alaph[str.at(i)]]);
            }
        }
        if (sum ==-1)
        {
            cout<<"error"<<endl;
        } 
        else
        {
            cout<<sum<<endl;
        }
    }

    return 0;
}