【華爲機試在線訓練】四則運算

題目

請實現如下接口

/* 功能：四則運算

 * 輸入：strExpression：字符串格式的算術表達式，如: "3+2*{1+2*[-4/(8-6)+7]}"

     * 返回：算術表達式的計算結果

 */

public static int calculate(String strExpression)

{

    /* 請實現*/

    return 0;

} 

約束：

pucExpression字符串中的有效字符包括[‘0’-‘9’],‘+’,‘-’, ‘*’,‘/’ ,‘(’， ‘)’,‘[’, ‘]’,‘{’ ,‘}’。

pucExpression算術表達式的有效性由調用者保證; 

輸入描述:

輸入一個算術表達式

輸出描述:

得到計算結果

示例1
輸入

3+2*{1+2*[-4/(8-6)+7]}

輸出

25

思路

C++代碼

#include<iostream>
#include<string>
#include<vector>
#include<stack>

using namespace std;

int main() 
{
	string s;
	while (cin >> s) 
	{
		stack<char> opera;
		vector<int> numcnt;
		string s1;
		for (int i = 0; i<s.size(); i++) 
		{
			if (s[i] >= '0'&&s[i] <= '9') 
			{
				int tmp = 0;
				while (s[i] >= '0'&&s[i] <= '9') 
				{
					tmp++;
					s1 += s[i];
					i++;
				}
				i--;
				numcnt.push_back(tmp);
			}
            
			else if (s[i] == '-' || s[i] == '+') 
			{
				if (s[i] == '-' && (s[i - 1] == '(' || s[i - 1] == '[' || s[i - 1] == '{'))
					s1 += '0';
				while (!opera.empty() && (opera.top() == '*' || opera.top() == '/' || opera.top() == '+' || opera.top() == '-')) 
				{
					s1 += opera.top();
					opera.pop();
				}
				opera.push(s[i]);
			}
            
			else if (s[i] == '*' || s[i] == '/') 
			{
				while (!opera.empty() && (opera.top() == '*' || opera.top() == '/')) 
				{
					s1 += opera.top();
					opera.pop();
				}
				opera.push(s[i]);
			}
            
			else if (s[i] == '(' || s[i] == '[' || s[i] == '{')
				opera.push(s[i]);
            
			else if (s[i] == ')') 
			{
				while (opera.top() != '(') 
				{
					s1 += opera.top();
					opera.pop();
				}
				opera.pop();
			}
            
			else if (s[i] == ']') 
			{
				while (opera.top() != '[') 
				{
					s1 += opera.top();
					opera.pop();
				}
				opera.pop();
			}
            
			else if (s[i] == '}') 
			{
				while (opera.top() != '{') 
				{
					s1 += opera.top();
					opera.pop();
				}
				opera.pop();
			}
            
			else
				cout << "Invalid input!" << endl;
		}
        
		while (!opera.empty()) 
		{
			s1 += opera.top();
			opera.pop();
		}
		stack<int> nums;
		int ind = 0;
		for (int i = 0; i<s1.size(); i++) 
		{
			if (s1[i] >= '0'&&s1[i] <= '9') 
			{
				int total = 0;
				while (numcnt[ind]--)
					total = 10 * total + (s1[i++] - '0');
				i--;
				nums.push(total);
				ind++;
			}
            
			else 
			{
				int tmp1 = nums.top();
				nums.pop();
				int tmp2 = nums.top();
				nums.pop();
				if (s1[i] == '+')
					nums.push(tmp2 + tmp1);
				else if (s1[i] == '-')
					nums.push(tmp2 - tmp1);
				else if (s1[i] == '*')
					nums.push(tmp2*tmp1);
				else
					nums.push(tmp2 / tmp1);
			}
		}
		cout << nums.top() << endl;
	}
}