uva 442 矩阵链乘

最新推荐文章于 2022-09-12 00:24:25 发布

chenhongwei6447

最新推荐文章于 2022-09-12 00:24:25 发布

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本文链接：https://blog.youkuaiyun.com/chenhongwei6447/article/details/48275099

// 题意：输入n个矩阵的维度和一些矩阵链乘表达式，输出乘法的次数。假定A和m*n的，B是n*p的，那么AB是m*p的，乘法次数为m*n*p

// 算法：用一个栈。遇到字母时入栈，右括号时出栈并计算，然后结果入栈。因为输入保证合法，括号无序入栈

//  Created by Chenhongwei in 2015.
//  Copyright (c) 2015 Chenhongwei. All rights reserved.

#include"iostream"
#include"cstdio"
#include"cstdlib"
#include"cstring"
#include"climits"
#include"queue"
#include"cmath"
#include"map"
#include"set"
#include"vector"
#include"stack"
#include"sstream"
#include"algorithm"
using namespace std;
typedef long long ll;
typedef pair<int,int> P;
P m[30];
int main()
{	
	//ios::sync_with_stdio(false);
	// freopen("in.txt","r",stdin);
	//freopen("out.txt","w",stdout);
	int n;
	scanf("%d\n",&n);
	for(int i=1;i<=n;i++)
	{
		char ch;
		int a,b;
		scanf("%c %d %d\n",&ch,&a,&b);
		m[ch-'A'+1].first=a;
		m[ch-'A'+1].second=b;
	}
	string s;
	while(getline(cin,s))
	{
		stack<P> stk;
		ll ans=0;
		int flag=1;
		for(int i=0;i<s.size();i++)
		{
			if(s[i]=='(')continue;
			else if(isalpha(s[i]))
				stk.push(m[s[i]-'A'+1]);
			else if(s[i]==')')
			{
				P x,y,temp;
				x=stk.top();stk.pop();
				y=stk.top();stk.pop();
				if(x.first!=y.second)
				{
					flag=0;
					printf("error\n");
					break;
				}
				else
				{
					ans+=y.first*y.second*x.second;
					temp.first=y.first;
					temp.second=x.second;
					stk.push(temp);
				}
			}
		}
		if(flag==1)
			cout<<ans<<endl;
		


	}
	
	return 0;
}