中序表达式变成后序表达式 JAVA实现版本

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package algorithm;import java.util.*;public class ConvertMiddleOrder2PostOrder {   /*    *     * convert middleOrder math expression to PostOrde    * for example: A-B*(C+D)/E (in-order)    * converted result: ABCD*E/- (post-oder)    */   public static String ConvertInOrder2PostOrderUtil(String inOrderString){    //support:  + - * /     /* element content:     * l = <     * g = >     * e = =     * n = not available      * each operation map to array index:      * + =   0     * - =   1     * * =   2     * / =   3     * for example: oprPriority[2][3]=‘e',  就是 operator * 跟栈类的  /比较优先级，结果是优先级 相等。     * (, ),比较特殊，就在代码中处理了。     */        char [][] oprPriority = new char[][]{     {'e','e','l','l'},     {'e','e','l','l'},     {'g','g','e','e'},     {'g','g','e','e'}     };     if(inOrderString.length()<3) {    System.out.println("bad expression data");    return null;    }        char[] resultarray = new char[inOrderString.length()];    int rstindex=0;    int len=inOrderString.length();    int curposition=0;        //save operators    Stack<String> mystack = new Stack<String>();    char[] tmparray = new char[2];    char stackchar,curchar;    while(len>0){    System.out.println("converted str="+new String(resultarray));    curchar=inOrderString.charAt(curposition);    switch(curchar) {    case '0':    case '1':    case '2':    case '3':    case '4':    case '5':    case '6':    case '7':    case '8':    case '9':    resultarray[rstindex++]=curchar;    curposition++;    len--;    break;    case '+':    case '-':    case '*':    case '/':    if(!mystack.empty()){       //compare operation    tmparray=mystack.peek().toCharArray();        if(tmparray[0]=='(') {        //push this operator as '(' in stack is lowest    tmparray[0]=curchar;    mystack.push(new String(tmparray));    curposition++;    len--;        } else {         int column,row;         switch(curchar){            case '+':            row=0;            break;        case '-':        row=1;            break;        case '*':        row=2;            break;        case '/':        row=3;            break;            default:            System.out.println("expression error");        return null;         }         switch(tmparray[0]){            case '+':            column=0;            break;        case '-':        column=1;            break;        case '*':        column=2;            break;        case '/':        column=3;            break;            default:            System.out.println("expression error");        return null;         }                 char result=oprPriority[row][column];        switch(result){         case 'g': // incoming > operator in stack            //push this operator if it is higher than stack top    tmparray[0]=curchar;    mystack.push(new String(tmparray));    curposition++;    len--;    break;         case 'e': //=         case 'l': // <            //pop up the top operator in stack            mystack.pop();            resultarray[rstindex++]=tmparray[0];        break;         default:            System.out.println("expression error");        return null;         }       }            } else {    //push this operator    tmparray[0]=curchar;    mystack.push(new String(tmparray));    curposition++;    len--;    }        break;        case '(':    //push into stack    tmparray[0]=curchar;    mystack.push(new String(tmparray));    curposition++;    len--;    break;        case ')':    //pop up all operator until it meet '('    while(!mystack.empty()){    tmparray=mystack.peek().toCharArray();    mystack.pop();    if(tmparray[0]=='('){    break;    } else {      //save this operator to result str      resultarray[rstindex++]=tmparray[0];    }    }    curposition++;    len--;        break;    default:    System.out.println("expression error");    return null;    }        }        while(!mystack.empty()) {    tmparray=mystack.pop().toCharArray();    resultarray[rstindex++]=tmparray[0];    System.out.println("converted str="+new String(resultarray));    }String result=new String(resultarray);return result;}}
测试语句：
ConvertMiddleOrder2PostOrder.ConvertInOrder2PostOrderUtil("1-2*(3+4)/5"))
//output is
converted post-order expression is: 1234+*5/-
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