uva442Matrix Chain Multiplication（栈）

题目链接：

lrj--p141。

#include<iostream>
#include<cstdio>
#include<cstring>
#include<string>
#include<stack>
#include<cctype>
using namespace std;

struct matrix
{
    int a,b;
    matrix (int x=0,int y=0):a(x),b(y) {}
}m[26];
int main()
{
    int n;
    char ch;
    string ss;
    while(scanf("%d",&n)!=EOF&&n)
    {
        for(int i=0;i<n;i++)
        {
            cin>>ch;
            scanf("%d%d",&m[ch-'A'].a,&m[ch-'A'].b);
        }
       while( cin>>ss )
        {
            int ans=0;
            int ok=0;
            stack<matrix> s;
            while(!s.empty()) s.pop();
            int len=ss.length();
            for(int i=0;i<len;i++)
            {
            if(isalpha(ss[i])) s.push(m[ss[i]-'A']);
            else if(ss[i]==')')
            {
                matrix m2=s.top();
                s.pop();
                matrix m1=s.top();
                s.pop();
                if(m1.b!=m2.a) {ok=1;break;}
                ans+=m1.a*m1.b*m2.b;
                s.push(matrix(m1.a,m2.b));
            }

        }
        if(!ok) printf("%d
",ans);
        else puts("error");
    }
    }
}