Codeforces 552E Vanya and Brackets（贪心 + 表达式计算）

#include <bits/stdc++.h>

using namespace std;

#define rep(i, a, b)	for (int i(a); i <= (b); ++i)
#define dec(i, a, b)	for (int i(a); i >= (b); --i)

typedef long long LL;

vector <int> pos;



LL calc(const string &str){

	stack <LL>   num;
	stack <char>  op;

	for (int i = 0, slen = str.length(); i < slen; ++i) {
		if (str[i] == ‘)‘){
			while (op.top() != ‘(‘){
				LL tmp = num.top();
				num.pop();
				if (op.top() == ‘*‘) num.top() *= tmp;
				else if (op.top() == ‘+‘) num.top() += tmp;
				op.pop();
			}
			op.pop();
			continue;
		}
		if (isdigit(str[i])) num.push(str[i] - ‘0‘);
		else if (str[i] == ‘+‘ && !op.empty() && op.top() == ‘*‘){
			while (!op.empty() && op.top() == ‘*‘){
				LL tmp = num.top();
				num.pop();
				num.top() *= tmp;
				op.pop();
			}
			op.push(str[i]);
		} 
		else op.push(str[i]);
	}
	while(!op.empty()){
		LL tmp = num.top();
		num.pop();
		if(op.top() == ‘*‘) num.top() *= tmp;
		else if(op.top() == ‘+‘) num.top() += tmp;
		op.pop();
	}
	return num.top();
}

int main(){

	string str;
	cin >> str;
	pos.push_back(-1);
	int slen = str.length();
	for (int i = 1; i < slen; i += 2) if (str[i] == ‘*‘) pos.push_back(i);
	pos.push_back(slen);
	slen = pos.size();

	LL ret = INT_MIN;
	rep(i, 0, slen - 2)
		rep(j, i + 1, slen - 1){
			string s = str;
			s.insert(pos[i] + 1, 1, ‘(‘);
			s.insert(pos[j] + 1, 1, ‘)‘);
			ret = max(ret, calc(s));
		}
	cout << ret << endl;
	return 0;
}