/// <summary>
/// 逆波兰-中缀表达式转换为后缀表达式
/// </summary>
/// <param name="expression">中缀表达式</param>
/// <returns></returns>
public Queue <EvalItem> ParserInfixExpression(string expression)
{
var queue = new Queue <EvalItem>();
var operatorStack = new Stack <OperatorChar>();
int index = 0;
int itemLength = 0;
int expressionLength = expression.Length;
//当第一个字符为+或者-的时候
char firstChar = expression[0];
if (firstChar == AddOprator || firstChar == SubOperator)
{
expression = string.Concat("0", expression);
}
using (var scanner = new StringReader(expression))
{
string operatorPreItem = string.Empty;
while (scanner.Peek() > -1)
{
char currentChar = (char)scanner.Read();
switch (currentChar)
{
case AddOprator:
case SubOperator:
case DivOperator:
case MulOperator:
case LBraceOperator:
case RBraceOperator:
//直接把数字压入到队列中
operatorPreItem = expression.Substring(index, itemLength);
if (operatorPreItem != "")
{
var numberItem = new EvalItem(EItemType.Value, operatorPreItem);
queue.Enqueue(numberItem);
}
index = index + itemLength + 1;
itemLength = -1;
//当前操作符
var currentOperChar = new OperatorChar()
{
Operator = currentChar
};
if (operatorStack.Count == 0)
{
operatorStack.Push(currentOperChar);
break;
}
//处理当前操作符与操作字符栈进出
var topOperator = operatorStack.Peek();
//若当前操作符为(或者栈顶元素为(则直接入栈
if (currentOperChar == LBraceOperatorChar || topOperator == LBraceOperatorChar)
{
operatorStack.Push(currentOperChar);
break;
}
//若当前操作符为),则栈顶元素顺序输出到队列,至到栈顶元素(输出为止,单(不进入队列,它自己也不进入队列
if (currentOperChar == RBraceOperatorChar)
{
while (operatorStack.Count > 0)
{
var topActualOperator = operatorStack.Pop();
if (topActualOperator != LBraceOperatorChar)
{
var operatorItem = new EvalItem(EItemType.Operator, topActualOperator.GetContent());
queue.Enqueue(operatorItem);
}
else
{
break;
}
}
break;
}
//若栈顶元素优先级高于当前元素，则栈顶元素输出到队列,当前元素入栈
if (topOperator.Level > currentOperChar.Level || topOperator.Level == currentOperChar.Level)
{
var topActualOperator = operatorStack.Pop();
var operatorItem = new EvalItem(EItemType.Operator, topActualOperator.GetContent());
queue.Enqueue(operatorItem);
while (operatorStack.Count > 0)
{
var tempTop = operatorStack.Peek();
if (tempTop.Level > currentOperChar.Level || tempTop.Level == currentOperChar.Level)
{
var topTemp = operatorStack.Pop();
var operatorTempItem = new EvalItem(EItemType.Operator, topTemp.GetContent());
queue.Enqueue(operatorTempItem);
}
}
operatorStack.Push(currentOperChar);
}
//当当前元素小于栈顶元素的时候，当前元素直接入栈
else
{
operatorStack.Push(currentOperChar);
}
break;
default:
break;
}
itemLength++;
}
}
//剩余无符号的字符串
if (index < expressionLength)
{
string lastNumber = expression.Substring(index, expressionLength - index);
var lastNumberItem = new EvalItem(EItemType.Value, lastNumber);
queue.Enqueue(lastNumberItem);
}
//弹出栈中所有操作符号
if (operatorStack.Count > 0)
{
while (operatorStack.Count != 0)
{
var topOperator = operatorStack.Pop();
var operatorItem = new EvalItem(EItemType.Operator, topOperator.GetContent());
queue.Enqueue(operatorItem);
}
}
return(queue);
}
public static string GetContent(this OperatorChar opChar)
{
return(opChar.Operator.ToString());
}