LeetCode -- Basic Caculator

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public class Solution {
public int Calculate(string s) 
{
	// two stack
	var opStack = new Stack<string>();
	var numStack = new Stack<int>();
	var n = "";
	// if number , push number stack
	for(var i = 0;i < s.Length; i++){
		if(s[i] == ‘ ‘){
			continue;
		}
		
		// if (, +,- , push op stack
		if(s[i] == ‘(‘ || s[i] == ‘+‘ || s[i] == ‘-‘){
			opStack.Push(s[i].ToString());
		}
		// if ).  pop op stack, pop 2 from number stack, until reach ‘(‘
		else if(s[i] == ‘)‘){
			var poped = false;
			if(opStack.Count > 0 && opStack.Peek() == "("){
				poped = true;
				opStack.Pop();
			}
			
			while(opStack.Count > 0 && opStack.Peek() != "("){
				var n1 = numStack.Pop();
				var n2 = numStack.Pop();
				var o = opStack.Pop();
				numStack.Push(Calc(n1, n2, o));
			}
			if(!poped && opStack.Count > 0 && opStack.Peek() == "("){
				opStack.Pop();
			}
			
		}
		// push num into numStack, try calc until reach ‘(‘
		else
		{
			// parse out number 
			var valid = "0123456789";
			if(valid.Contains(s[i])){
				n += s[i];
				if(i == s.Length - 1 || !valid.Contains(s[i+1])){
					numStack.Push(int.Parse(n));
					n = "";
					while(opStack.Count > 0 && opStack.Peek() != "(")
					{
						var o = opStack.Pop();
						var n1 = numStack.Pop();
						var n2 = numStack.Pop();
						numStack.Push(Calc(n1,n2,o));
					}
					
				}
			}
		}
	}
	
	// pop the rest ops in opstack and numbers in number stack	
	while(opStack.Count > 0){
		var o = opStack.Pop();
		if(o != "+" && o != "-"){
			continue;
		}
		var n1 = numStack.Pop();
		var n2 = numStack.Pop();
		numStack.Push(Calc(n1,n2,o));
	}
	
	return numStack.Pop();
}
	
public int Calc(int n1, int n2, string op){
	switch(op)
	{
		case "+" :
			return n1 + n2;
		case "-" :
			return n2 - n1;
		default :
		throw new NotSupportedException();
	}
}


}

LeetCode -- Basic Caculator

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原文地址：http://blog.csdn.net/lan_liang/article/details/48649985