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  1. /* package whatever; // don't place package name! */
  2.  
  3. import java.util.*;
  4. import java.lang.*;
  5. import java.io.*;
  6.  
  7. /* Name of the class has to be "Main" only if the class is public. */
  8. class Ideone
  9. {
  10. 	public static void main (String[] args) throws java.lang.Exception
  11. 	{
  12. 		System.out.println(eval("2^3^2")); // this should be 512, i.e. 2^(3^2)
  13. 		System.out.println(eval("2*3^2")); // this should be 18, i.e. 2*(3^2)
  14. 	}
  15. static double eval(final String str) {
  16.     return new Object() {
  17.         int pos = -1, ch;
  18.  
  19.         void nextChar() {
  20.             ch = (++pos < str.length()) ? str.charAt(pos) : -1;
  21.         }
  22.  
  23.         boolean eat(int charToEat) {
  24.             while (ch == ' ') nextChar();
  25.             if (ch == charToEat) {
  26.                 nextChar();
  27.                 return true;
  28.             }
  29.             return false;
  30.         }
  31.  
  32.         double parse() {
  33.             nextChar();
  34.             double x = parseExpression();
  35.             if (pos < str.length()) throw new RuntimeException("Unexpected: " + (char)ch);
  36.             return x;
  37.         }
  38.  
  39.         // Grammar:
  40.         // expression = term | expression `+` term | expression `-` term
  41.         // term = factor | term `*` factor | term `/` factor
  42.         // factor = `+` factor | `-` factor | `(` expression `)`
  43.         //        | number | functionName factor | factor `^` factor
  44.  
  45.         double parseExpression() {
  46.             double x = parseTerm();
  47.             for (;;) {
  48.                 if      (eat('+')) x += parseTerm(); // addition
  49.                 else if (eat('-')) x -= parseTerm(); // subtraction
  50.                 else return x;
  51.             }
  52.         }
  53.  
  54.         double parseTerm() {
  55.             double x = parseFactor();
  56.             for (;;) {
  57.                 if      (eat('*')) x *= parseFactor(); // multiplication
  58.                 else if (eat('/')) x /= parseFactor(); // division
  59.                 else if (eat('^')) x = Math.pow(x, parseFactor()); //exponentiation -> Moved in to here. So the problem is fixed
  60.                 else return x;
  61.             }
  62.         }
  63.  
  64.         double parseFactor() {
  65.             if (eat('+')) return parseFactor(); // unary plus
  66.             if (eat('-')) return -parseFactor(); // unary minus
  67.  
  68.             double x;
  69.             int startPos = this.pos;
  70.             if (eat('(')) { // parentheses
  71.                 x = parseExpression();
  72.                 eat(')');
  73.             } else if ((ch >= '0' && ch <= '9') || ch == '.') { // numbers
  74.                 while ((ch >= '0' && ch <= '9') || ch == '.') nextChar();
  75.                 x = Double.parseDouble(str.substring(startPos, this.pos));
  76.             } else if (ch >= 'a' && ch <= 'z') { // functions
  77.                 while (ch >= 'a' && ch <= 'z') nextChar();
  78.                 String func = str.substring(startPos, this.pos);
  79.                 x = parseFactor();
  80.                 if (func.equals("sqrt")) x = Math.sqrt(x);
  81.                 else if (func.equals("sin")) x = Math.sin(Math.toRadians(x));
  82.                 else if (func.equals("cos")) x = Math.cos(Math.toRadians(x));
  83.                 else if (func.equals("tan")) x = Math.tan(Math.toRadians(x));
  84.                 else throw new RuntimeException("Unknown function: " + func);
  85.             } else {
  86.                 throw new RuntimeException("Unexpected: " + (char)ch);
  87.             }
  88.  
  89.             //if (eat('^')) x = Math.pow(x, parseFactor()); // exponentiation -> This is causing a bit of problem
  90.  
  91.             return x;
  92.         }
  93.     }.parse();
  94. }
  95. }
Success #stdin #stdout 0.06s 28092KB
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64.0
36.0
https://ideone.com/iN2mMa
language:
Java (HotSpot 12)
created:
5 years ago
visibility:
public

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