leetcode224

Basic Calculator

折腾了好一会儿，其实意思很简单。就是实现一个包含+，-法和括号运算的计算器。

可能是没找对方法吧，看了网上的代码量，感觉我写的就是一坨屎啊。。。参考：http://blog.youkuaiyun.com/xudli/article/details/46554835

每次压栈都是当前的结果，这样计算量会小很多。不过比较起来大神的代码比较简单，我的思路还是比较清晰的。

我的代码：

class Solution {
public:
	int calculate(string s) {
		stack<int>myStack;
		stack<char>myOperator;
		int i;
		for (i = 0; i<s.length(); i++)
		{
			while (i < s.length() && s[i] == ' ')
				i++;
			if (i == s.length())
				break;
			if (s[i] == '+' || s[i] == '-' || s[i] == '(')
				myOperator.push(s[i]);
			else if(s[i] == ')')
			{
				while ( myOperator.top() != '(')
				{
					int element1 = myStack.top();
					myStack.pop();
					int element2 = myStack.top();
					myStack.pop();
					char op = myOperator.top();
					myOperator.pop();
					if (op == '+')
						myStack.push(element1 + element2);
					else if (op == '-')
						myStack.push(element2 - element1);
				}
				if (!myOperator.empty())
					myOperator.pop();
				while (!myOperator.empty() && (myOperator.top() != '('))
				{
					int element1 = myStack.top();
					myStack.pop();
					int element2 = myStack.top();
					myStack.pop();
					char op = myOperator.top();
					myOperator.pop();
					if (op == '+')
						myStack.push(element1 + element2);
					else if (op == '-')
						myStack.push(element2 - element1);
				}
			}
			else
			{
				//myStack.push(getNumber(s, i));
				long long int number = 0;
				int j = i;
				while (j<s.length() && (s[j]-'0'<=9)&&(s[j]-'0'>=0))
				{
					number = number * 10 + (s[j] - '0');
					j++;
				}
				i = j - 1;
				myStack.push(number);
				while (!myOperator.empty() && (myOperator.top() != '('))
				{
					int element1 = myStack.top();
					myStack.pop();
					int element2 = myStack.top();
					myStack.pop();
					char op = myOperator.top();
					myOperator.pop();
					if (op == '+')
						myStack.push(element1 + element2);
					else if (op == '-')
						myStack.push(element2 - element1);
				}
				//if (!myOperator.empty())
					//myOperator.pop();
			}
		}
		return myStack.top();
	}
};