87 lines
1.8 KiB
Java
87 lines
1.8 KiB
Java
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import javax.script.*;
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import java.util.LinkedList;
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public class ExpressionParserShuntingYard {
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static boolean isDelim(char c) {
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return c == ' ';
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}
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static boolean isOperator(char c) {
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return c == '+' || c == '-' || c == '*' || c == '/' || c == '%';
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}
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static int priority(char op) {
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switch (op) {
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case '+':
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case '-':
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return 1;
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case '*':
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case '/':
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case '%':
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return 2;
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default:
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return -1;
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}
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}
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static void processOperator(LinkedList<Integer> st, char op) {
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int r = st.removeLast();
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int l = st.removeLast();
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switch (op) {
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case '+':
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st.add(l + r);
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break;
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case '-':
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st.add(l - r);
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break;
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case '*':
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st.add(l * r);
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break;
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case '/':
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st.add(l / r);
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break;
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case '%':
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st.add(l % r);
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break;
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}
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}
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public static int eval(String s) {
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LinkedList<Integer> st = new LinkedList<>();
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LinkedList<Character> op = new LinkedList<>();
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for (int i = 0; i < s.length(); i++) {
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char c = s.charAt(i);
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if (isDelim(c))
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continue;
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if (c == '(')
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op.add('(');
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else if (c == ')') {
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while (op.getLast() != '(')
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processOperator(st, op.removeLast());
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op.removeLast();
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} else if (isOperator(c)) {
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while (!op.isEmpty() && priority(c) <= priority(op.getLast()))
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processOperator(st, op.removeLast());
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op.add(c);
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} else {
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String operand = "";
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while (i < s.length() && Character.isDigit(s.charAt(i)))
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operand += s.charAt(i++);
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--i;
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st.add(Integer.parseInt(operand));
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}
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}
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while (!op.isEmpty())
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processOperator(st, op.removeLast());
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return st.get(0);
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}
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public static void main(String[] args) throws Exception {
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ScriptEngine engine = new ScriptEngineManager().getEngineByName("JavaScript");
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String exp = "1+2*3*4+3*(2+2)-100";
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System.out.println(eval(exp));
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System.out.println((Integer) engine.eval(exp) == eval(exp));
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}
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}
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