jcalbe3ed51
initial commit
+151 −0
2 files changed
- A Calculator.java +8 −0
- A Parser.java +143 −0
| @@ -0,0 +1,8 @@ | |||
| 1 | + | public class Calculator { | |
| 2 | + | public static void main(String[] args) { | |
| 3 | + | String expr = "(36 * 3 + 9 * 7) * (84 / 12) * 5"; | |
| 4 | + | Parser p = new Parser(expr); | |
| 5 | + | String postfix = p.toPostFix(); | |
| 6 | + | System.out.println(p.evalExpr(postfix)); | |
| 7 | + | } | |
| 8 | + | } | |
| @@ -0,0 +1,143 @@ | |||
| 1 | + | /* Todo | |
| 2 | + | * - Fix Substraction errors | |
| 3 | + | * - Add support for trigonometric functions | |
| 4 | + | * - Remove all edge cases | |
| 5 | + | */ | |
| 6 | + | ||
| 7 | + | import java.util.Stack; | |
| 8 | + | import java.util.StringJoiner; | |
| 9 | + | ||
| 10 | + | public class Parser { | |
| 11 | + | private String expr; | |
| 12 | + | private Stack<Character> operatorStack; | |
| 13 | + | ||
| 14 | + | public Parser(String infixExpr) { | |
| 15 | + | expr = infixExpr.trim().replaceAll("\\s", ""); // remove whitespaces | |
| 16 | + | } | |
| 17 | + | ||
| 18 | + | public static boolean isOperand(char c) { | |
| 19 | + | switch (c) { | |
| 20 | + | case '1': | |
| 21 | + | case '2': | |
| 22 | + | case '3': | |
| 23 | + | case '4': | |
| 24 | + | case '5': | |
| 25 | + | case '6': | |
| 26 | + | case '7': | |
| 27 | + | case '8': | |
| 28 | + | case '9': | |
| 29 | + | return true; | |
| 30 | + | default: | |
| 31 | + | return false; | |
| 32 | + | } | |
| 33 | + | } | |
| 34 | + | ||
| 35 | + | public static boolean isOperand(String c) { | |
| 36 | + | return isOperand(c.charAt(0)); | |
| 37 | + | } | |
| 38 | + | ||
| 39 | + | public int getPresedence(char c) { | |
| 40 | + | switch (c) { | |
| 41 | + | case '^': | |
| 42 | + | return 3; | |
| 43 | + | case '/': | |
| 44 | + | return 2; | |
| 45 | + | case '*': | |
| 46 | + | return 2; | |
| 47 | + | case '+': | |
| 48 | + | return 1; | |
| 49 | + | case '-': | |
| 50 | + | return 1; | |
| 51 | + | default: | |
| 52 | + | return -1; | |
| 53 | + | } | |
| 54 | + | } | |
| 55 | + | ||
| 56 | + | public boolean hasLeftAssociativity(char c) { | |
| 57 | + | if (c == '^') { | |
| 58 | + | return false; | |
| 59 | + | } else { | |
| 60 | + | return true; | |
| 61 | + | } | |
| 62 | + | } | |
| 63 | + | ||
| 64 | + | public String toPostFix() { | |
| 65 | + | operatorStack = new Stack<>(); | |
| 66 | + | StringJoiner output = new StringJoiner(" "); | |
| 67 | + | StringBuilder operand = new StringBuilder(); | |
| 68 | + | char[] infix = expr.replaceAll(" ", "").toCharArray(); | |
| 69 | + | ||
| 70 | + | // Main Expression Iteration | |
| 71 | + | for (int i = 0; i < infix.length; i++) { | |
| 72 | + | char c = infix[i]; | |
| 73 | + | if (isOperand(c)) { | |
| 74 | + | operand.append(infix[i]); | |
| 75 | + | if (i < infix.length - 1) { | |
| 76 | + | continue; | |
| 77 | + | } | |
| 78 | + | } | |
| 79 | + | ||
| 80 | + | if (operand.length() > 0) { | |
| 81 | + | output.add(operand.toString()); | |
| 82 | + | operand = new StringBuilder(); | |
| 83 | + | } | |
| 84 | + | ||
| 85 | + | if (c == '(') { | |
| 86 | + | operatorStack.push(c); | |
| 87 | + | } else if (c == ')') { | |
| 88 | + | while (!operatorStack.isEmpty() && operatorStack.peek() != '(') { | |
| 89 | + | output.add(operatorStack.pop().toString()); | |
| 90 | + | } | |
| 91 | + | operatorStack.pop(); | |
| 92 | + | } else { | |
| 93 | + | while (!operatorStack.isEmpty() && getPresedence(c) <= getPresedence((char) operatorStack.peek()) | |
| 94 | + | && hasLeftAssociativity(c)) { | |
| 95 | + | output.add(operatorStack.pop().toString()); | |
| 96 | + | } | |
| 97 | + | operatorStack.push(c); | |
| 98 | + | } | |
| 99 | + | } | |
| 100 | + | ||
| 101 | + | while (!operatorStack.isEmpty()) { | |
| 102 | + | if (operatorStack.peek() == '(') { | |
| 103 | + | return "This expression is invalid"; | |
| 104 | + | } | |
| 105 | + | output.add(operatorStack.pop().toString()); | |
| 106 | + | } | |
| 107 | + | ||
| 108 | + | // last digit gets duplicate entry for some reason, so have to remove it. | |
| 109 | + | String op = output.toString(); | |
| 110 | + | return op.substring(0, op.length() -2); | |
| 111 | + | } | |
| 112 | + | ||
| 113 | + | private Double evaluate(String operator, Double op1, Double op2) { | |
| 114 | + | switch (operator.charAt(0)) { | |
| 115 | + | case '+': | |
| 116 | + | return op2 + op1; | |
| 117 | + | case '-': | |
| 118 | + | return op2 - op1; | |
| 119 | + | case '*': | |
| 120 | + | return op2 * op1; | |
| 121 | + | case '/': | |
| 122 | + | return op1 / op2; | |
| 123 | + | case '^': | |
| 124 | + | return (Math.pow(op2, op1)); | |
| 125 | + | default: | |
| 126 | + | return 0.0; | |
| 127 | + | } | |
| 128 | + | } | |
| 129 | + | ||
| 130 | + | public double evalExpr(String postfix) { | |
| 131 | + | Stack<Double> stack = new Stack<Double>(); | |
| 132 | + | for (String c : postfix.split(" ")) { | |
| 133 | + | if (isOperand(c)) { | |
| 134 | + | stack.push(Double.parseDouble(c)); | |
| 135 | + | } else { | |
| 136 | + | Double op1 = (Double) (stack.pop()); | |
| 137 | + | Double op2 = (Double) (stack.pop()); | |
| 138 | + | stack.push(evaluate(c, op2, op1)); | |
| 139 | + | } | |
| 140 | + | } | |
| 141 | + | return stack.pop(); | |
| 142 | + | } | |
| 143 | + | } | |