四则运算脚本解析计算
1.个位数的加减法运算
记住前一位的加号或减号运算符，使用加号或减号用运算符后面的数字改变累加值。
package yuki.arithmetic.script;
public class SingleDigitTest {
public static void main(String[] args) {
String s1 = "1+2+3+4+5+6+7+8+9";
System.out.println(s1 + "=" + calculate(s1));
String s2 = "1-2+3+4-5+6+7-8+9";
System.out.println(s2 + "=" + calculate(s2));
}
private static int calculate(String s) {
char[] cs = s.toCharArray();
char oper = ‘+‘;
int result = 0;
for (int i = 0; i < cs.length; i++) {
char c = cs[i];
if(c == ‘+‘ || c == ‘-‘){
oper = c;
}else if(‘0‘ <= c && c <= ‘9‘) {
int x = c - ‘0‘;
switch (oper) {
case ‘+‘:
result += x;
break;
case ‘-‘:
result -= x;
break;
}
}
}
return result;
}
}
运行结果如下：
1+2+3+4+5+6+7+8+9=45 1-2+3+4-5+6+7-8+9=15
2.使用脚本引擎计算
java提供的脚本解析工具，如果解析的脚本是javascript脚本，实现类是RhinoScriptEngine。
package yuki.arithmetic.script;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;
public class ScriptEngineTest {
public static void main(String[] args) throws ScriptException {
ScriptEngineManager engineManager = new ScriptEngineManager();
ScriptEngine engine = engineManager.getEngineByName("javascript");
String script = "1*2*3*4*5*6*7*8*9";
Object result = engine.eval(script);
System.out.println(script + " = " + result);
System.out.println(script + " = " + 1*2*3*4*5*6*7*8*9);
}
}
运行结果如下：
1*2*3*4*5*6*7*8*9 = 362880.0 1*2*3*4*5*6*7*8*9 = 362880
3.带括号的四则运算
方便测试，上一行使用的是下文的四则运算解析，下一行使用的是javascript的脚本解析。
为了避免计算错误输入的脚本，所以在计算前做了去除空白字符，验证脚本是否输入规范。
从后往前的解析脚本，这与正常的计算顺序一致，因为使用了递归，都是把前面的结果算完了再和后面的结果操作。
如果是从前往后的解析脚本，途中出现减号，后面的算式作为一个括号中的整体参与减法，导致计算错误。
package yuki.arithmetic.script;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;
public class ResolverDemo {
public static void main(String[] args) throws ScriptException {
String s1 = "1+2+(3+4)+(5+(6*7+8))+9";
System.out.println(calculate(read(s1)));
System.out.println(evalScript(s1));
String s2 = "1+2+(3/4)+(5+(6*7+8/9))";
System.out.println(calculate(read(s2)));
System.out.println(evalScript(s2));
String s3 = "((1+(2+(3/4))+(5+(6*78+9))))";
System.out.println(calculate(read(s3)));
System.out.println(evalScript(s3));
String s4 = "1-(2-(3/4))+(5-(-6*7*8+9))";
System.out.println(calculate(read(s4)));
System.out.println(evalScript(s4));
String s5 = "-12*3 + 4*56 - (7 + 8*9)/(2*3)";
System.out.println(calculate(read(s5)));
System.out.println(evalScript(s5));
}
public static Object evalScript(String script){
ScriptEngine engine = new ScriptEngineManager().getEngineByName("javascript");
try {
return engine.eval(script);
} catch (ScriptException e) {
e.printStackTrace();
return -1;
}
}
public static String read(String s){
s = s.replaceAll("\\s+", "");
char[] cs = s.toCharArray();
for (int i = 0, j = 1; j < cs.length; ++i, ++j)
if((cs[i] == ‘+‘ || cs[i] == ‘-‘ || cs[i] == ‘*‘ || cs[i] ==‘/‘) &&
(cs[j] == ‘+‘ || cs[j] == ‘-‘ || cs[j] == ‘*‘ || cs[j] ==‘/‘))
throw new RuntimeException("运算符相邻");
int deep = 0;
for (char c : cs) {
if(c == ‘(‘)
++ deep;
else if(c == ‘)‘)
-- deep;
}
if(deep != 0)
throw new RuntimeException("左右括号不等");
return s;
}
public static double calculate(String s){
char[] cs = s.toCharArray();
if(cs.length == 0)
return 0;
int pos = -1;
if((pos = plusPos(cs)) != -1){
char oper = cs[pos];
double left = calculate(s.substring(0, pos));
double right = calculate(s.substring(pos + 1));
if(oper == ‘+‘)
return left + right;
else if(oper == ‘-‘)
return left - right;
}else if((pos = timesPos(cs)) != -1){
char oper = cs[pos];
double left = calculate(s.substring(0, pos));
double right = calculate(s.substring(pos + 1));
if(oper == ‘*‘)
return left * right;
else if(oper == ‘/‘)
return left / right;
}else{
if(cs[0] == ‘(‘ && cs[cs.length - 1] == ‘)‘){
return calculate(s.substring(1, cs.length - 1));
}else{
int y = 0;
for (char c : cs)
if(‘0‘ <= c && c <= ‘9‘)
y = y*10 + (c - ‘0‘);
if(cs[0] == ‘-‘)
y *= -1;
return y;
}
}
return 0;
}
private static int plusPos(char[] cs) {
int deep = 0;
for (int i = cs.length - 1; i >= 0 ; --i) {
char c = cs[i];
switch (c) {
case ‘(‘:
++deep;
break;
case ‘)‘:
--deep;
break;
case ‘+‘:
case ‘-‘:
if(deep == 0)
return i;
break;
}
}
return -1;
}
private static int timesPos(char[] cs) {
int deep = 0;
for (int i = cs.length - 1; i >= 0 ; --i) {
char c = cs[i];
switch (c) {
case ‘(‘:
++deep;
break;
case ‘)‘:
--deep;
break;
case ‘*‘:
case ‘/‘:
if(deep == 0)
return i;
break;
}
}
return -1;
}
}
运行结果如下：
74.0 74.0 51.638888888888886 51.638888888888886 485.75 485.75 331.75 331.75 174.83333333333334 174.83333333333334
本文地址：http://www.cnblogs.com/kodoyang/p/Arithmetic_ScriptResolve_Calculate.html
雨木阳子
2015年8月29日
时间： 2024-08-01 18:21:28