UVa 442

题意

矩阵链乘
求乘法次数

思路

利用栈<结构体>
遇到字母入栈, 遇到 ‘)’ 出栈并计算, 结果再次入栈

AC代码

#include <iostream>
#include <cstdio>
#include <string>
#include <stack>

using namespace std;

struct matrix
{
    int a, b;
}m[30], m1, m2, mm;

stack<matrix> stk;

int main()
{
    int T;
    char c;
    string s;
    scanf("%d",&T);
    getchar();
    while(T--){
        scanf("%c ",&c);
        //m[c-'A'].name = c;
        scanf("%d %d",&m[c-'A'].a,&m[c-'A'].b);
        getchar();
    }
    int re, len;
    bool err;
    while( cin >> s ){
        re = 0;
        len = s.length();
        err = false;
        for( int i = 0; i < len; i++ ){
            if( isalpha(s[i]) )
                stk.push( m[s[i]-'A'] );
            else if( s[i] == ')' ){
                m2 = stk.top();
                stk.pop();
                m1 = stk.top();
                stk.pop();
                if( m1.b != m2.a ){
                        //cout << "*  " << m1.b << "  " << m2.a <<endl;
                    err = true;
                    break;
                }
                re += m1.a * m1.b * m2.b;
                mm.a = m1.a, mm.b = m2.b;
                stk.push(mm);
            }
        }
        if(err) cout << "error" << endl;
        else    cout << re << endl;
        while(!stk.empty())
            stk.pop();
    }
    return 0;
}