使用计算机求算术的方法

题解

使用计算机求算术的方法

代码

#include <iostream>
#include <stack>
#include <map>
#include <cstring>
using namespace std;
stack<int>num;
stack<char>sign;
map<char, int>priority;
char s[1000009];
inline void gaochushuzi(char* s, int &lenth, int &return_num)
{
	lenth = 0;
	int signal = 1;
	const char *p = s;
	int tmp = 0;
	if (*p == '-')
	{
		signal = -1;
		p++;
		lenth++;
	}
	while (1)
	{
		
		
		if (*p >= '0' && *p <= '9')
		{
			tmp = tmp * 10 + (*p - '0');
			p++;
			lenth++;
		}
		else
		{
			return_num = tmp * signal;
			return;
		}

	}
}
int main()
{
	priority['+'] = 0;
	priority['-'] = 0;
	priority['*'] = 1;
	cin >> s;
	int lenth = 0;
	lenth = strlen(s);
	for (int i = 0; i < lenth; )
	{
		{
			int lenth;
			int ret;
			gaochushuzi(s + i, lenth, ret);
			num.push(ret);
			i += lenth;
		}

		if (sign.empty())//如果符号位为空，那么push符号
		{
			if (s[i] == 0)
			{
				cout << num.top()%10000 << endl;
				return 0;
			}
			
			sign.push(s[i]);
			i++;
		}
		else
		{
			int tmp = s[i];
			{
				if (tmp == 0)//表示结束
				{
					while(num.size()!=1)
					{//计算
						int ans = 0;
						int b = num.top();
						num.pop();
						int a = num.top();
						num.pop();
						char op = sign.top();
						sign.pop();
						switch (op)
						{
						case '+':
							ans = a + b;
							break;
						case '-':
							ans = a - b;
							break;
						case '*':
							ans = a * b;
							break;
						}
						ans %= 10000;
						num.push(ans);
					}
					cout << num.top() << endl;
					return 0;
				}

			}
			if (priority[tmp] > priority[ sign.top()])
			{
				sign.push(tmp);
				i++;
			}
			else 
			{
				while (sign.size() != 0 && priority[tmp] <= priority[sign.top()])
				{
					{//计算
						int ans = 0;
						int b = num.top();
						num.pop();
						int a = num.top();
						num.pop();
						char op = sign.top();
						sign.pop();
						switch (op)
						{
						case '+':
							ans = a + b;
							break;
						case '-':
							ans = a - b;
							break;
						case '*':
							ans = a * b;
							break;
						}
						ans %= 10000;
						num.push(ans);
					}
				}
				sign.push(tmp);
				i++;
			}
		}
	}
	return 0;
}