带括号的加减乘除--递规算法.(java.)-优快云博客

本文介绍了一个简单的数学表达式解析和计算程序。该程序能够处理包含加减乘除及括号的数学表达式，通过逐字符扫描的方式进行解析，并利用递归消除括号内表达式，最终计算出表达式的值。

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package com.livedoor.gl.core.bean.util;

import java.util.ArrayList;
import java.util.List;

public class oper {

private void printList(List<String> l, String desc) {
  /**
  System.out.println(desc + "'s size:" + l.size());
  for (Iterator iter = l.iterator(); iter.hasNext();) {
   String e = (String) iter.next();
   System.out.println(e);
  }**/
}

private boolean isDiget(char f) {
  if (f >= '0' && f <= '9')
   return true;
  if (f == '.')
   return true;
  return false;
}

private boolean isOperation(char f, char before) {
  if(f=='(' || f==')')
   return true;
  if (f == '+' || f == '/' || f == '*')
   return true;
  if (f == '-' )
   if((before == ')' || isDiget(before)))
    return true;
   else
    return false;

  return false;
}

private boolean isOperation(String element) {
  if (element.length() == 1) {
   if (element.equals("+") || element.equals("-")
     || element.equals("*") || element.equals("/"))
    return true;
   if(element.equals(")") || element.equals("("))
    return true;
  }
  return false;
}

private boolean isOperationJJ(String element) {
  if (element.length() == 1) {
   if (element.equals("+") || element.equals("-")) {
    return true;
   }
  }
  return false;
}

private boolean isOperationCC(String element) {
  if (element.length() == 1) {
   if (element.equals("*") || element.equals("/")) {
    return true;
   }
  }
  return false;
}

private List<String> getList(String source) {
  List ret = new ArrayList<String>();
  char[] cArr = source.toCharArray();
  String tmp = "";
  for (int i = 0; i < cArr.length; i++) {
   char before = 'x';
   if (i != 0)
    before = cArr[i - 1];
   if (this.isOperation(cArr[i], before)) {
    if(!tmp.equals(""))
     ret.add(tmp);
    tmp = "";
    ret.add("" + cArr[i]);
   } else {
    tmp += "" + cArr[i];
   }
  }
  if(!tmp.equals(""))
   ret.add(tmp);
  return ret;
}

private double caculateTwoNumber(String oper, String leftNum,
   String rightNum) {
  double ret = 0;
  if (oper.equalsIgnoreCase("+")) {
   ret = Double.valueOf(leftNum).doubleValue()
     + Double.valueOf(rightNum).doubleValue();
  } else if (oper.equalsIgnoreCase("-")) {
   ret = Double.valueOf(leftNum).doubleValue()
     - Double.valueOf(rightNum).doubleValue();
  } else if (oper.equalsIgnoreCase("*")) {
   ret = Double.valueOf(leftNum).doubleValue()
     * Double.valueOf(rightNum).doubleValue();
  } else if (oper.equalsIgnoreCase("/")) {
   ret = Double.valueOf(leftNum).doubleValue()
     / Double.valueOf(rightNum).doubleValue();
  }
  return ret;
}

private void caculateJJCC(List<String> source) {

  if (source.size() == 1)
   return;

  int offset = 0;
  Object[] oArr = source.toArray();
  for (int i = 0; i < oArr.length; i++) {
   String sss = (String) oArr[i];
   if (this.isOperationCC(sss)) {
    double result = this.caculateTwoNumber(sss, source
      .get(offset - 1), source.get(offset + 1));
    source.set(offset, "" + result);
    source.remove(offset + 1);
    source.remove(offset - 1);
    offset -= 2;
   }
   offset++;
  }

  this.printList(source, "tmpList CC ed.");

  offset = 0;
  String[] oArr2 = (String[])source.toArray(new String[source.size()]);
  for (int i = 0; i < oArr2.length; i++) {
   String sss = (String) oArr2[i];
   if (this.isOperationJJ(sss)) {
    double result = this.caculateTwoNumber(sss, source
      .get(offset - 1), source.get(offset + 1));
    source.set(offset, "" + result);
    source.remove(offset + 1);
    source.remove(offset - 1);
    offset -= 2;
   }
   offset++;
  }
  this.printList(source, "source JJ ed.");
  }

private int findLastedLeftKuohao(List<String> source) {
  if (!source.contains("("))
   return -1;
  return source.lastIndexOf("(");
}

@SuppressWarnings("unchecked")
private void caculateKuohao(List<String> source) {
  // 从source中找到最左面的左括号。到最近的右括号。取得startIndex,endIndex.并截取subList.
  int startIndex = this.findLastedLeftKuohao(source);
  int endIndex = 0;
  List sub = null;
  if (startIndex != -1) {
   List tmp = source.subList(startIndex, source.size());
   int rightIndex = tmp.indexOf(")");
   if (rightIndex != -1) {
    sub = tmp.subList(0, rightIndex + 1);
   }
   endIndex += startIndex + rightIndex;
   this.caculateJJCC(sub);
   source.remove(startIndex + 2);
   source.remove(startIndex);
  } else {
   this.caculateJJCC(source);
  }
  // 判断，如果仍就有括号。就再次递归。否则，就退出。
  if (this.findLastedLeftKuohao(source) != -1) {
   this.caculateKuohao(source);
  } else {
   this.caculateJJCC(source);
   return;
  }
}

public String getResult(String fun){
  List l = this.getList(fun);
  this.caculateKuohao(l);
  return (String)l.get(0);
}

/**
* @param args
*/
public static void main(String[] args) {
  oper client = new oper();
  System.out.println(client.getResult("7*2+(8*6)"));
}

}