题解 | #表达式求值#

// HJ54-2 表达式求值.cpp : 此文件包含 "main" 函数。程序执行将在此处开始并结束。
#include<iostream>
#include<bits/stdc++.h>

using namespace std;

int ComputerNum(string& s, int left, int right)
{
	char op = '+';
	vector<int>dp;
	int num = 0;
	int len = s.size();
	for (int i = left; i <=right; i++)
	{
		if (isdigit(s[i]))
		{
			num = num * 10 + s[i] - '0';
		}
		if (s[i] == '(')
		{
			int layer = 0;
			int j = i;
			while (j <=right)
			{
				if (s[j] == '(')
				{
					layer++;
				}
				else if (s[j] == ')')
				{
					layer--;
					if (layer == 0)
					{
						break;
					}
				}
				j++;
			}
			num = ComputerNum(s, i + 1, j - 1);
			i = j + 1;
		}
		if (!isdigit(s[i])||i==right)
		{
			switch (op)
			{
			case '+':dp.push_back(+num); break;
			case '-':dp.push_back(-num); break;
			case '*':dp.back() *= num; break;
			case '/':dp.back() /= num; break;
			}
			op = s[i];
			num = 0;
		}
	}
	int res = 0;
	for (auto c : dp)
	{
		res += c;
	}
	return res;
}

int main()
{
	string s;
	while (cin >> s)
	{
		int len = s.size();
		cout << ComputerNum(s, 0, len-1)<<endl;
	}
	return 0;
}