java 中缀转后缀（逆波兰）[通俗易懂]

import java.util.Stack;


public class LeetCode_middleTransformToReversePolish {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		String[] input={"9","+","(","3","-","1",")","*","3","+","10","/","2"};
		System.out.println(middleToBack(input));

	}
	
	public static String middleToBack(String[] input)
	{
		int length=input.length;
		String result="";
		boolean isHaveleftToken=false;
		Stack<String> stack=new Stack<>();
		for(int i=0;i<length;i++)
		{
			if(!isOperator(input[i]))
				result=result+input[i];
			else {
				if(stack.isEmpty())
					stack.push(input[i]);
				else if(input[i].equals("*")||input[i].equals("/"))
				{
					String tempeek=stack.peek();
					if(isHaveleftToken)
						stack.push(input[i]);
					else {
						if(tempeek.equals("*")||tempeek.equals("/"))
							result=result+stack.pop();
						
						stack.push(input[i]);
						
					}
				}
				else if(input[i].equals("("))
				{
					isHaveleftToken=true;
					stack.push(input[i]);
				}
				else if(input[i].equals(")"))
				{
					String temp=stack.pop();
					while(!temp.equals("("))
					{
						result=result+temp;
						temp=stack.pop();
						
					}
					isHaveleftToken=false;
					
				}
				else {
					if(isHaveleftToken)
						stack.push(input[i]);
					else {
						while(!stack.isEmpty())
							result=result+stack.pop();
						stack.push(input[i]);
					}
					
				}
						
				
			}
		}
		//加上栈中还没出栈的元素
		while(!stack.isEmpty())
		{
			result=result+stack.pop();
		}
		
		return result;
		
	}
	
	 public static boolean isOperator(String s) 
	 {
		 if(s.equals("+")||s.equals("-")||s.equals("*")||s.equals("/")||s.equals("(")||s.equals(")"))
			 return true;
		 else
			 return false;
	 }

}